In the dim and distance past, I used to get my bike serviced in a place where they had the following menu on the wall -
Servicing - £40 per hour
If you wait, £50 per hour
If you watch, £60 per hour
If you've worked on it yourself, £70 per hour
If you offer to help out, £80 per hour
Needless to say I took the loan bike and scooted away asap
You could try Essential Rubber, they're good honest guys