BMW E60 key replacement

[DeanR32]

Evening all

I need to replace the keyfob for my car as the middle (lock) button doesn't work and it's a pain in the arse having to go round, let the boy out and go back round to lock it.

I think it works out roughly 170 from BMW so wondered if anyone has a cheaper way of doing it.

I've seen replacement fobs on eBay but how do I go about coding the thing?

Any help will be appreciated

Cheers