Free: Contests & Raffles.
I would be doing a little research before offering to help anyone build a gun, especially after I594. It's perfectly acceptable to build your own... key words being "build your own". There have been cases where people were having others finish the 80% lowers for them, and it didn't work out so well for either party.
People have had visits from ATF for letting people use their mills to finish lowers. Big boy rules here, just being friendly.http://www.calguns.net/calgunforum/showpost.php?p=10982758&postcount=1