You may be able to get by with only one UPC number, there are a number of providers that sell you individuals under their manufacturing ID. UPCcode.net is one that I know of.
A manu ID is $700 or so through UCC, but since you won't be selling at retail, you can use this workaround.
However, if you ever plan to expand into retail or have multiple products/lines, its probably better to bite the bullet and get your own UPC manufacturing ID. You also have to have a bulletproof system to track the utilization of the numbers. Once assigned, you can't reuse it. But a manu ID gives you a bank of numbers to use.
Beware of print quality. Amazon charges for bad scans as its the basis for their Warehousing system.
Email me if you have any other questions
Randy G
Metagistics Corporation