£36 isnt that much although I agree it's alot more than they will have cost to make. It's a small price to pay compared with what can happen if you run a set of wheels with the incorrect centre bore without them.
The issue I have with "universal" spacers is they are normally poorly manufactured cheap tatt. They can cause no end of issues when fitted that you just dont get with a good quality set that are made for a specific application. If your middle names are "heath" & "robinson" then crack on but I'd suggest you give them a wide birth.