Having looked at the Nikon lens compatibility chart here:
http://www.nikonians.org/nikon/slr-lens.html
I can see that there's some fairly significant restrictions on using the older lenses on your D50 (assuming that you have a D50), or using the D50 lens on an FM/FE body. Under these circumstances, I can understand why the K1000 is being recommended. The Pentax K1000 is bullet proof (I have one), can be had - complete with 50mm 'standard' lens - for well under your $200 budget and will hold its value well so you could sell it again for the same kind of money as you paid for it after you've finished your class, if you wanted. If you go down the Pentax route and are looking at body+lens combinations on offer, the f/1.7 or f/1.4 50mm lenses are better than the more common f/2 lens, but the f/2 is no slouch and not to be disregarded. Here's
an example
Regards,
Duncan