Shooting Pentax since my first Spotmatic in 1971, and digital since 2005,I have a lot of gear, more than I can use.
You seem to be on a budget.
If so, you should first check which wide angle focal length suits you best by using your kit DA 18-55. It is an entry level lens, but yet a good one, capable of delivering nice pictures; it has pleasing IQ, better if you correct its aberrations, either in-camera if you shoot JPEG, or using a lens profile in computer PP. Using your 18-55, you will also appreciate the accuracy and convenience of AF.
You could do what many photography professors recommand: set your 18-55 zoom on a selected focal length, and shoot your subject with this focal length. You can even stick the zooming ring with adhesive tape! :)
Try 18, 20, 21, 31, 35, 40, 43, it will give you a very good idea of what the matching prime will deliver. The prime will be sharper, of course, but stopped f8, DA 18-55 is already quite sharp..The main difference will be the prime will allow wider aperture, hence better subject isolation (more bokeh) at focal lengths longer than 30.
If 18 is too narrow, then you may appreciate the DA15. It is a very nice lens, small and with unique rendering, but really wide: it is a love or hate! As for me, I love it.
The focal lengths between 21 and 50 are the most useful IMO. 70/77 are already telephoto lenses on APS-C, excellent for portrait or details in landscapes or architecture.
DA 35-macro is a true macro which doubles as a very nice landscape and general purpose lens. But remember that macro in the field is limited by your ability to come very close and be steady much more than by the lens performance. It is almost impossible to go to 1/1 ratio without a tripod.
I have the DA limiteds 15, 21, 35 Macro, 70, and the 40XS, they are very nice lenses but rather expensive. The difference between kit DA 18-55 and a bunch of limited primes is like the difference between a basic Chevrolet or Toyota and a upper model Audi, Mercedes or Porsche: all these cars will drive you to destination in about the same time, but it wont be the same experience....
The full frame limited FA31, FA43 and FA77 are even more expensive. My son Nicolas06 has already told you how all these lenses behave. I also have DA35 f2.4, and FA50 f1.7, which I bought used, and both are very good.
Cannot speak for the DA20-40 limited but I have the DA 17-70 f4 zoom, it is very good lens, sharp, and faster than most entry level zooms at the long end. Big and heavy, too IMO, hence I often go with DA 18-135 (not so good IQ, but lighter, smaller, more versatile for my way of shooting).
To sum it up: possibilities are infinite, it will be your decision, but you will soon see that 700$/€ budget is not that much when it comes to buying lenses, and you better avoid to buy a lens that you wont use.
