I paid a pennies short of £11k for mine (different cars, but pretty much the same job) for a good job by someone who knows what they're doing.

I know of Cossie'd RST done the same, but a couple of years earlier which was £7.5k

And a Cossie'd Orion again IRO £11k

Obviously it'd be a lot cheaper if you did it yourself, but personally I wouldn't want to get involved in a task like that, slightest error and you could be in deep shit.