Get the cheap replacement. If it works, job done. If it doesn't, it didn't cost much. Take the old one with you to make sure right size/shape., obv.

Nothing special about them, except they aren't made in such quantities as regular room lighting, hence more expensive.

7 quid? pah! I've just ordered an Epson projector lamp! £219.10 + VAT!
(just as a spare in case the current one dies inconveniently)

A.