[RickM]

This is what I do:

Start a credit card account with Fedex or UPS...you may be able to do the same with USPS. Get whatever free packaging you can from the courier you choose to use....usually envelopes, boxes and labels. I also have access to boxes here at work so that helps a bit.

I use Fedex as they're the most convenient (they have small offices ALL over) and they typically come in as the cheapest.

As mentioned you will need to have the recipients address in order to make an accurate cost estimate.

I use a high quality bathroom scale for 2+ pounds and a more precise mail scale for smaller items. I weigh the completely packaged product and enter it into the estimator on the carrier website. This will give you a good idea of the cost...you can always buffer a little if you want to protect yourself from underestimating. Remember to log into the carriers website as the rates for a person with an account will be a bit lower.

When the sale is complete you can enter the destination info (unless you saved it from the estimate) and print out the bar coded mailing label. Attach the label to the package using the free self stick pouch they provide. Then you merely drop the package off at the office/depot...no waiting in lines.

Don't worry if your estimate is a bit off. When the package is processed the carrier will make adjustments as needed and bill your credit card accordingly.

If you don't have the recipients address there are a couple of approaches. Some will estimate the cost to the the furthest destination in the US from their location and charge that amount....obviously it'll be on the high side.
Others will find a mid point and use that amount...figuring that the cost will average out.
The benefit to the averaging is that you can have a cost advertised up front and check-out can take place quickly and with less work on the sellers part.