My wife turned me onto PirateShip.com for buying and printing one-off shipping labels.
Pirate Ship was new to me but I just used it to get some cars out to folks and it is nice and easy. They claim to have lower rates than USPS direct, and while I think my postage was less, it wasn't much...but I'll take what I can get!
More so, however, is it's great to be able to print my shipping labels at home and then just treat the post office as a drop-off. My PO is usually pretty busy to wait in line, and the self-serve kiosk in the lobby isn't much faster (when it's working). And for whatever reason, the USPS site doesn't let you print first class postage for your own boxes.
Eitherway, it's worth checking out if you do any amount of shipping - even the one-off postage we often do for our races. It's free to use (at this point) and honestly, I can't complain about anything right now. I'm gonna ride the ship until it goes away or starts charging me more. Your mileage may vary but Pirate Ship is worth a look.
This is NOT a sponsored post or anything of that nature. It's me honestly sharing a site that might save you a few bucks on shipping. I'm not any compensation or kickbacks from the vendor or the link, (or anyone else, for that matter).