If you go to a small town DMV, you should have no problems. But try doing the same in a big city DMV and they'll throw the book at you.
I live close to a small town, and one time I bought an almost brand new GSXR750 and went to register it and said that I had paid $500 for the bike. The lady didn't even flinch. She either new nothing about bikes or just didn't give a crap about her job
BTW, if you claim a low purchase price here in CA, you don't get hammered by the registration and taxes.