You should ask if he's open to that and see how much value he places in your contribution. I've been in his shoes to some extent, but in the end what matters is

You should ask if he's open to that and see how much value he places in your contribution. I've been in his shoes to some extent, but in the end what matters is his perception of the cash trade off and to what extent he wants to get you committed to the company. If he is open to it, ask what he thinks it would be worth as a % and what form it would take (options, restricted stock, ...). If you do reach an agreement for equity in lieu of pay, be sure to get good contracts in place. It's impossible to know all the twists and turns that can come along when you are doing a start up and you'll want to ensure your contribution and sacrifice are rewarded.