To save money, see
https://www.pentaxforums.com/forums/pentax-lens-articles/152336-cheap-macro-b...lose-work.html
To spend money, a 'dedicated' macro lens is nice. 35-40-50-55mm lenses require working CLOSE, which means that it's easy to fill the frame, but such short focal lengths are best for studio work. 90-100-105mm lenses (or longer) give more working room, better for field shooting.
AF on any macro lens isn't for macro work, but for using the lens for general photography. Many folks get 90-100-105mm AF lenses to use for portraits or short tele work also. But real close up, AF is not your friend. For general-purpose shooting, AF is great. For macro, read on.
AF or A-type lenses have an advantage over manual-aperture lenses: you can shoot with P-TTL flash. When shooting such lenses on P-TTL-only cameras like most of our modern dSLRs, flash is just a bit trickier. Not impossible, as seen in
yeatzee's spectacular work, just trickier.
More iris blades don't really matter at macro range. More blades are nice for general photography. Many of my cheap enlarger lenses have 15 blades. But one of my favourites is the Schneider Betavaron 50-125mm enlarger zoom with with just 5 blades, brutally sharp with good bokeh.
So, how much to spend depends on how hard you want to work, and with what light. I can put a 105/3.5 enlarging lens (US$20) on my M42 Bellowscope bellows (US$20) shooting with ambient or controlled light, and get images just as good as with a rather costlier AF macro lens.
EDIT: I can also put an Industar-50/3.5 (US$25) on a set of M42 macro tubes (US$6) and get superb 1:1 shots.