They're not made for use "in conjunction with eBay or PayPal", but the Seiko and Dymo laber printers are wonderful for one-off label printing. Copy, paste, print. That's it. Very professional looking, as well. They're pricy but, in the case of the Seiko printers at least, they keep going and going and going. I set up 2 of them in a medium-size law office about 11 or 12 years ago, and I recently found out that they're still going strong, printing 50 to 100 labels per day. These were the Seiko SLP Pro and the 220.
If you look around on eBay you may get a sweet deal on one. If you factor the time saved printing labels plus the durability of the printers (which will give you a good resale value if you decide to sell it later on), you might be able to justify the expense.
Cheers,
Ernie.