You need to be more specific:
1. How does the startup salary compare to your current salary?
2a. What is the startup option package as a % of the company?
2b. What is the vesting schedule?
2c. Also --
(i) how big is the startup?
(ii) How much money have they raised?
(iii) Where is it based?
(iv) How much experience do you have?
With this information we can give ideas on what comparable companies offer.
You have several paths. The best way to negotiate the vested stocks is probably: "Over the next year, if I joined you guys, I would vest $X worth of public stocks. Therefore in order to join I would need a signing bonus of $X in order to compensate me for losing this."