You can already buy forever stamps at a discount on Ebay. Shop now (enter "forever stamps") and among other offers you'll find a "Buy it now" price of $2 for 5 stamps with free shipping.
After spending some time there, I'd say that's certainly an interesting category of eBay. There are folks selling single stamps near face value with free shipping. WTF?? And they have thousands of positive feedback transactions so this is definitely legit.