Userscript - Update the price for 'used and new' items on Amazon product pages to include delivery/p&p. Also shows each seller's full price (including delivery/p&p) on the Amazon 'used and new' tab when opened.
Initially save static versions of pages under test for quick acceptance testing and guarantees that details such as price won't change. Additionally add tests that run against the actual site to detect changed layouts that break things.
Move away from userscripts.org (seems to be very spammed, is cumbersome to deploy to and not heavily used). Make the script portable as a FF/Chrome addon which wlll give greater exposure.