John Shriver , Mar 13, 2010; 02:17 p.m.
That's high. A ZX-5n from keh.com in Excellent+ condition is $105. (The MZ and ZX cameras are identical, different branding for different retail markets.)
Adorama's used prices are all over the map, some too high, some low. They (and B&H) are much more keen on new equipment.
That's an excellent choice from the Pentax autofocus film bodies. It has KAF2 mount, not crippled, so you can use any lens (other than the cropped-sensor "D" lenses) on it. The only more desirable autofocus film bodies are MZ-3/ZX-3 (rare as the dickens), and the top-of-the-line MZ-S (easy to find, but pricey).
The MZ-7/ZX-7 are also OK, but you don't get a shutter speed dial.
The Pentax-F and Pentax-FA primes are fetching quite high prices for use on Pentax digital cameras. You can't really get any of them for less than $300, many are $600 and more. The cheaper -F and -FA zooms can be very good value, since their ranges are awkward on cropped-sensor digital bodies.