Originally posted by Roob-N-Boots Like everybody said a DA 35 2.4 would be a good choice. If you think an F50f1.7 would be more usefull try searching Ebay for old film cameras that might come bundled with one such as SF1,SF1N etc. I got my F50 1.7 with a SF1 for $200 shipped, both in brand new condition but I have seen them go for as low as $135 together.
I got my F50/1.7 attached to a K1000. I was in too much of a hurry to complete the transaction to ask why.
Not too many AF primes sell for $200. I can only think of a couple of other ones that come close.
There's a 100mm f3.5 macro made by Cosina. It's sold under the Vivitar, Phoenix and even Pentax brand. It's optically very good, but feels cheap because all of the focusing parts are plastic, the only lens I've seen like that. Also available in manual focus versions. With a little shopping you might find it for less than $200. Get the diopter that allows 1:1 magnification.
There's a Sigma 24mm f2.8. This one is usually sold for over $200 in its AF version, but close enough I think. It's pretty sharp wide open, a very useful focal length, a good companion to a DA-L 35/2.4. Its biggest problem is flare - some reviews are dramatic on this point - but this is a very good lens. Also in manual focus versions, which I have.
You can use the Zenitar 16mm f2.8 fisheye as if it was an AF lens, because at f5.6 or f8, the depth of field is just about everything in front of you. So a potential kit of $200 AF-ish lenses: Zenitar 16mm fisheye, Sigma 24, DA-L 35, F50, Cosina 100 macro, all for less than an FA 31/1.8.