How big are the parts? how many? while it's probably not the most environmentally sound idea, I use gasoline

but only for small parts, and NOT in a parts washer!

paint thinner, mineral spirits, etc. are all like $10-15 a gallon. Gas is "cheap" at $3.xx a gallon around here....this week.

for small parts, I pour some out into an oil catch pan, and use a paint brush. while I'm sitting outside in the gravel driveway. away from anything electrical.

then I let the parts sit and dry outside.

if it's something that needs painted, follow up the gas bath with a shot of brake cleaner and you're good to go. I've not had any problems with it

The little bit that I let evaporate up into the air or pour onto the driveway where it quickly evaporates each year, is nothing compared to the amount of gas that gets spilled at the gas station from people topping off their tanks or overfilling jerry cans on the ground, so I don't feel THAT bad for "wasting" the gas that way