You don't have to do it for each sale.

You just customise the template and eBay pull the relevant data onto the template.

You can then print out a combined address label / invoice. All you have to do is fold it, place it in an invoice enclosed envelope and stick it to the parcel with the customers address showing. Quick and easy to do as it saves having to write out the buyers address.

For your return address you can buy 1000 address labels for around $20.00 so you just stick them on as well.