I used to do it in australia, so the prices will differ, but £10m2 sounds VERY cheap considering the work involved. Was it a total refurb with cutting disc and a repolish?
If so, then whoever charged £1000 will probably have a few machines going and alot of labour..
I know how you feel mate. Could you do it for the same money though? Thats the question, if not, then why undersell yourself, just wait for the phonecall for you to come fix the mistake afterwards