The K1000 is still a popular choice among students yet was the most basic of the K series and can sell for pretty silly prices.

A better choice IMO would be the Pentax KM (a K1000 with self timer and depth of field preview - otherwise identical), it's less well known, but, with DOF preview, is a FAR better camera and tends to sell for less than the K1000 for some strange reason.

Better still would be a KX, if you can find one. This also has Mirror Lock-Up, a better viewfinder with both aperture and shutter speed displayed and a different meter which can be switched off. The KX does seem to be pretty scarce though.