[robjmitchell]

Unfortunately you are going to need two lenses. Chasing wildlife unfortunately requires large and expensive telephoto lenses. The 55-300 is as good as you will get in a budget option.
The second lens covering wide angle to short telephoto is usually called a walk around lens.
There are several different options.
pentax 18-135wr, weather sealed with very good centre performance, not very wide and weaker in the corners. very good for long zoom range and lightweight.
Pentax 17-70/4, constant f4 aperture but not weather sealed, SDM motor issues. wouldn't buy second hand.
Pentax 18-85wr, Best image quality and wider, but pricey.
Sigma 17-70 (three models) very good image quality, no WR and no pentax rendering but a good step up from kit lens (18-55)
Hope this helps

[Des]

But I am also getting a bit sick and tired of swapping lenses (and its been only 6 months). The aforementioned lenses are all hand me downs from my pa, they are all manual focus, and I seem to be getting better at it, but really if there was a lens that could take a similar level of quality to the SMC Pentax-A 1:1.7 yet have auto focus and zoom past a perceived depth that the stock can manage... then that's prolly more up my street than just a 'zoom' lens.

All these choices involve compromises, as you have probably gathered from all the helpful posts above. There is no single lens that can do everything you want: a standard of photos in the wide-normal range that gives a similar level of quality to your primes, and sufficient telephoto reach for photographing wildlife.

You have to choose which is more important to you:
1. having a single lens that provides most of the coverage you want, or
2. having two lenses that provide coverage out to 300mm and better quality images (particularly when the light is not great) than option 1.

Option 1 means one of the 18-250 (Tamron, Pentax or Sigma) or 18-270 (Pentax) superzooms. A second-hand version of any of these would be within your budget (although used copies of the 18-270 are hard to find). (Sigma now make an 18-300 but it costs >$500.) These are quite good lenses for what they are; the image quality is at least as good as, and probably better than, the kit lenses. The versatility and convenience are their main virtues, and those are considerable ones. The downsides are that they have a lot of distortion at the wide end (correctable if you shoot RAW and edit in post-processing), they are slow (that is, maximum aperture across the range is not very wide compared to zooms with a shorter range of focal lengths, which means not ideal in low light), and you need to stop down (that is, use a narrow aperture) if you want corner and edge sharpness. None of them is weather resistant. If you are shooting mostly in good light you can still get quite good results, particularly if you shoot in RAW and process the images afterwards.

Note that for photographing wildlife, the difference between a superzoom and a Pentax 55-300 is greater than it might seem. For one thing, the 55-300 is faster (ie greater maximum aperture) at the long (telephoto) end - which is helpful in shade or low light. Second, because of the way the lenses focus, the magnification on the superzooms is only as long as the numbers suggest (if at all) when focusing to infinity (which is uncommon). So when you focus at 250mm on a kangaroo 15m away, the magnification will be much less than it would be with the 55-300 at 250mm. This makes a big difference in photographing birds and other wildlife.

Even with option 2 (two lenses) you won't get both lenses within your budget. The best approach would be to get a 55-300 and use your 18-55 while saving up for one of the better walk-around zooms mentioned above. And even then, no walkaround zoom is going to provide the low-light performance or quite the same quality as your primes. But many of us find that good walk-around zooms do quite well enough for ordinary use, without need to switch to primes all the time. Having a weather-resistant lens (e.g. DA 16-85 or 18-135, or for a premium option the DA*16-50 f2.8) to go with your WR camera is a great bonus at times too.

You can get a second-hand DA or DA-L 55-300 for about $150-250. Keep an eye on the PF marketplace, Gumtree and ebay Australia. The DA is generally about $50-$100 more but some premium is worth it for quick shift (the ability to manually override the autofocus without switching to manual focus on the camera).

The latest WR version of the 55-300 (optically identical, except for improved coatings) would be better, but they are hard to find second hand in Australia and even then probably outside your budget. They cost more than $500 new.

[robgski]

The 55-300 is as good as you will get in a budget option.

FWIW, I take the 55-300 on walks in the woods, and at the 55mm end, its FOV is suitable, but being able to zoom in to an animal hiding in a thicket, or a bird high in a tree is very nice, and the image quality is very good.

The aforementioned lenses are all hand me downs from my pa, they are all manual focus, and I seem to be getting better at it

I won't suggest that AF is not convenient, and sometimes necessary, but trust me when I say that slowing down in order to nail the focus also helps improve composition and other elements of a great photograph. Otherwise, I find that too much reliance on AF turns my DSLR into an overpriced point and shoot. Also, consider getting familiar with zone focusing, especially with a zoom. The razor edge focus of a 50mm 1.8 is great for the types of shots you use a 50mm for, but most zooms flatten out the subject at extreme range, and razor thin focus means a less clear subject. Swapping lenses does get tiresome, that is why I often do an out and back route, choosing one lens out and switching to a second lens for the walk back.

[normhead]

Two suggestions come to mind, the DA 50 1.7 is extremely cheap right now, I've spent more on steaks for a barbecue at the supermarket. But if you are sick of changing lenses the Tamron 17-50 is a great lens that tests well against primes in every preference test I've done. It is also a nice low cost option.

If you can find one a Sigma 70-300 is a nice cheap lens, especially second and. I've seen them for a low as $80.

[Des]

Two suggestions come to mind, the DA 50 1.7 is extremely cheap right now, I've spent more on steaks for a barbecue at the supermarket.

It's an excellent lens and great value, but given that the OP has an A-50 f1.7 and a very tight budget, it probably wouldn't be the top priority.

To the OP: Despite this comment, most of the time, follow Norm's advice. Consider his suggestion for a Tamron 17-50 f2.8 as your walkaround lens if you want something not far from prime standard and fast enough for many low light conditions (e.g. indoors without flash). Norm also makes a strong case elsewhere for the 18-135 as a lens for the great outdoors - also excellent advice (I took it and I'm pleased).