payment page

I have my site exactly the way I want it. No errors at all. Now I have the index page as the place where you can sign up and register. When I click register, I have it going to a membership option page and then from there it goes to the registration form. The registration form works fine but the page before that is giving me problems. I have the menu named options_id and the same for the database. I have all the info in a separate file called register.php where it sends everything to the database. How do I send the options_id to the database? I want to have it so when the user fills out the register form it goes to my paypal for whichever options_id they choose. I have the values for them as 1, 2, 3, 4, and 0 for please select.