Call your local bar association; they can refer you to an appropriate lawyer. Have him review your current contract, and keep his contact info for reviewing any future contracts. Cost me about $200 last time I did this.

Large companies are less likely to let you change parts of the contract, but if a startup wants you they may.

If they don't want to change this provision, insist on getting all (or most) of your compensation in cash, not stock.

Ie only accept the job, if the cash alone is enough, treat the stock as worthless until proven otherwise.