Website HiJacked

I built a Flash website for a client.
Sent client a measely 3600$ invoice.
Client refuses to pay saying he had website appraised at $500 wouldn’t pay more than 1200$
I refuse and offer 3000$
Client changes password to the domain and hijacks my creative work.

Anyone have any advice?

Website in question is:
(if you View Source my name is in it.)


Also thinking about calling the domain host and filing a DMCA.