There is nothing stopping you from transferring the postage part of a payment into your eBay account, therefore effectively paying as you go.

The difference is that instead of it automatically being deducted from your Paypal account you have to click about three buttons. For a postage cost that is now considerably less than using any other AP service. Other than own packaging.

If, of course, your time is worth more than $120 per hour (assuming it takes 24 seconds to do 3 clicks for a satchel, comparing satchels) then go for it. Or work out what time it takes to find and package 'own'.

I'll use the eBay system thanks.