how long is a piece of string? you get what you pay for in the machine polishing game, £80-100 IMO will not give the fella enough time to do a FULL machine polish correctly, he could do an enhancement detail on just the paintwork for that in a day tho! (enhancement detail i class as one pass with the rotary with a fairly harsh polish, but no follow up refinement with a milder polish)

for a FULL machine polish (i.e. defect free, or as close as ) i would expect to pay around £250 including a good wax!