add one product for purchase, on 2 pages

I have a site that sells training reservations. The type of training is selected from a list and then on the training detail page there is a purchase button which goes directly to paypal where they make payment and the class is reserved. On the checkout page (training detail page) I want to offer a product as well, with a flat rate (increments by percentage for more than one quantity ordered), and sales tax. There will be no shipper or shipping API involved. That will be done manually. I just need to capture their name, address, etc. Mail is to go out to both the admin and customer who purchased when a sale goes through. Budget $75 I need this completed quickly!