Street vendors cannot use the word Celtic or Celtic crest / logo.
The street vendors sell badges at £2 each and some also do 3 for £5 for smaller badges. The larger are £3 each.
Take your time and browse the stalls. It is worth the time. Saves you bidding for the same badge on eBay. The vendors do not generally use eBay. They are normally sales by individuals who have bought them before a game.