"Free" boats usually fall into the "you get what you pay for" category, and in any case "free" is a misnomer.
If you can get a decent boat in decent shape for under $2G then I say go for it, but do what you can (ask around, get some expert advice on specific boat) to ensure that it, too, is not a waste of money. Spending on a survey is the best way, but at that price you may have a hard time justifying a $3-400 fee even though that is the way to go.
One thing to keep in mind - as a cheap starter boat it may be fine for a while... if this works out for you, "2-foot-itis" will rear its head in short order. Will you be stuck with a hard-to-sell knocker as you try to move up? One thing you don't want to be is a reluctant 2-boat owner.