I've never had a smell that I couldn't get rid of with bleach. I would try a soak in as concentrated bleach as you can afford.
or just throw some in there and shake it for a while. I've found it works quickly.
are these kegs new?
are they ball lock or pin lock?
40$ isn't very good, I can get a used 43$ pin lock online with shipping included, is there any way you can barter him down?