Quote: How on Earth do you work out the capital gains tax on each of these?
You make the best guess you can as to what you paid for them. As long as you try to be honest about it the IRS will probably accept it. If you aren't they may decide to value at face value for your starting basis.
Starting in 2022 as dictated by the current administration and the new 30K IRS agents they hired any sale of anything over $600 has to automatically be reported by any auction house including EBAY. starting at end of year you will need to provide to your auctioneer your I.D S.S Card and sign full tax paperwork for the government to get its 25% cut.