Acetone, available in quart-size tins at Home Depot, Wal-Mart, etc. for
under $5. Or maybe paint thinner, like the other poster said. Acetone's a
bit more expensive but I prefer it for many clean-up jobs.

Do not use acetone on plastic (it will melt the plastic). Also, it's not a
big deal if you don't wear gloves, but try to minimize getting it on your
hands. It dries out the oil in one's skin and is probably carcinogenic or
some other flavor of nasty "toxicity."