Nice camera equipment. I actually picked up a pristine Canon A1 with 50mm 1.8 attached last week for $25.
That lens probably isn't worth a great deal to flip but should be nice to use and for $4 why not :)
Always be on the look out for used lenses, the money is on the fast ones if that Sigma was a 2.8 it would be worth a lot more.
50mm in the 1.2 range are $$$ as well
With a growing M4/3 camera market a lot of people buy older fast glass and put on their digital cameras.