It depends on how good you are at what you do: If you are a really great developer and you become an vital part of the infrastructure after a few months, that will significantly increase your leverage. In order for this to work, you have to be able to walk out on the job for real if the negotiations don't go as planned. That just involves keeping feelers out for replacement jobs (always a good idea regardless when joining a startup since there's no guarantee the company will survive for long) and having enough money saved up to be out of work for a few months, and knowing how to apply for unemployment benefits if you need to.

If you suck well there's no guarantee that they will keep you anyways.

Main thing would be -- would you enjoy relocating to the west coast? If you never get any benefits other than the salary, would that be enough? Have you considered whether the place you are moving to might have higher/lower costs of living?