ASP Shopping Cart w/referal codes, coupons

What I need help with is shopping cart features for web site. I presently use PayPal Shops, which is very limited. I want to keep processing payment through paypal, but you need to accumulate an order format a whole string to send to PayPal so the buyer can checkout. The following are the desired elements which I think would make my cart project unique: - No sign-in. The user has already supplied PayPal with shipping info etc and I refuse to make him enter it again, nor do I want to give the user the impression I am compiling a customer database with him in it. - Redeem multiple coupons. I issue gift certificates. To redeem, the user would enter the unique ID from the certificate(s) in a box on the checkout screen. The cart would have to peek into my database and look-up the balance available for that coupon ID before proceeding. If the user entered $50 worth of Coupon IDs for a $45 order, the cart would have to store the remaining $5 back into my database against the last Coupon ID entered, as well as mark any other Coupon ID's as used up. - Referral Code. I'd like to let people enter a special code to get free shipping. The referral code belongs to a charity or a past customer. The referral code's owner gets credit for making the referral, so the cart would have to check if the code is listed in my database, and update the entry for credit owed to the referrer. - Pay by mail option. After the cart computed all the referrals and discounts, the user could say "I ain't buying - empty my cart" and the cart would have to put back all the coupon credits and referral credits. Likewise, the user could say "I'll pay by mail" in which case the user prints out the order and the cart still gets emptied. (When the mail order arrives, I would manually adjust my databases). I guess ideally, the coupon and referral database adjustments wouldn't actually be made to my database until PayPal sent back confirmation that the order was paid. - Threshold-based shipping charges. I sell everything from bumper stickers (class 1) to sweatshirts (class 3). The minimum s&h is $1, but if the user selects ANY items from class 2, the flat s&h jumps to $4, and if ANY class 3 item is selected, S&H = $7. If the cart is updated such that all class 3 items are removed, the S&H would have to jump back down to the appropriate level. Basically, I want a cart that tracks the order for the current session only and assigns it an order number, and puts the whole thing into my database. Then it passes the amount due and the order number to PayPal, which sends me the user's shipping detail for that order number if payment is made. I need features the user will see to check-out, and I guess I need an online interface for me to enter orders. I'd prefer to have this be compatible with FrontPage and coded in ASP language, since I could then possibly make minor changes myself. I hope you have enough detail here to quote the job. Architecture is most important. If I go over budget on coding, I'm willing to finish it myself. Cheers, -Ron