Before you decide how much to bid on an item have you searched round the internet for the lowest price available.
I buy and sell Postcards and CDs and the occasional item of historical interest for my local area.
Ebay doesn't allow links to places that you should be looking at before making a decision about how much to bid so using a search engine will bring up the main contenders for your wants. There is no point paying £20 for a used item you could have got brand new for £15.
A tip: Why not sign up for a points saving card and collect points whilst buying on Ebay.