Yeah they're not cheap but I bought cheap ones before and they didn't work. 2 festoon for the number plate, one for the central dome light in the front, and one for the boot. You could use another 2 for the vanity mirrors if you really wanted, I don't use them anyway. The boot one doesn't fit as the holder is too big, but a folded up piece of kitchen foil does the trick

I do have 2 spare led 501's if you're interested: bought them for the sidelights but apparently that would be illegal...