1) Site for sale: http://www.couponsitescript.com/
2) Asking Price (or if auction, starting bid plus end time in days): 49$ - basic coupon script. Plugins can be added at any time depending on your needs.
3) Payment method (ie: Paypal, Escrow etc): Paypal and Plimus
4) Additional Info, such as traffic details, revenue, cost of upkeep: Can go up to 4500$/month. However if you promote it more can go even more.
Cost of site: only the hosting and domain costs.