You already agreed to this via verbal contract to the $400 maximum. I'm not sure where some of the other guys can say you should do anything. Unless you stated

You already agreed to this via verbal contract to the $400 maximum. I'm not sure where some of the other guys can say you should do anything. Unless you stated you would keep on working for free after the $400 (which I think probably would be the softest point in the verbal agreement later even if you did), the best you can do is work until that contract expires and negotiate a better written one with equity. Let me repeat: you verbally agreed to work when he offered to "pay [you] to work on his project". You need to do the best you can to meet that agreement because you agreed to the deal. You need to return the contract to them and firmly state you did not agree to this during the verbal agreement. If he wants you to sign something more than you already verbally agreed, he has to negotiate. Be sure he understands you want equity opportunity during any renegotiation because you are interested in the site and want to continue to work to help it grow after the contract is over.