Its not good to put it this way, Now a days no one gives a damn, let alone offering you something in return for some money, i would rather appreciate the helping hand offered by this guy.
Will you be paying the employer share of Federal and State taxes from their paycheck? No
Is there any obligation or gurantee that you will help them in return for the work they have done for you? No.
If, after working for 3 months on your project; if you dont like them, will you still be obligated to finance them to work on their idea? No
That's the definition of someone looking for a temp or contract programmer. (and frankly, the market rate for a 3 month contract programmer of YC caliber would be at least double that).
So, was I mistaken? :) :)
Note the big difference. YC lends a helping hand by letting the startups work on their own projects and investing money, effort, experience and time to help them succeed with their companies.
My sincere suggestion is: be generous and offer the exact same terms that YC does.
"cast your bread upon the waters for after many days they shall return to you"