Have you already negotiated with them? (@techjuice brings up a great list of points which could be negotiated). Is the contract signed? Is 100k their first offer?
You could contact 10x Management (they offer "Agent on Demand"[1] which was discussed on HN[2]) for help / guidance. I've been represented by them for 5 years and they do tremendous work (they're professional agents / negotiators..!)
Email me if you want more info (email in profile). I'm Canadian and have been doing nothing but contract work for US customers for the past 5 years.