Tuition is fairly straighforeward, £25 gets you a couple of hours in a clas of ~8 or so. After that if your there all week just for surfing, look into buying a board, some of the smaller shops have second hand kit.
Avoid shopping for kit in towns, I made the mistake of going down whilst needing new rash vest, wrongly assuming that as everyone in cornwall surfs it would be as cheep as anywehre. I was duly parted with £25 for soemthing thats £5 from decathlon!
Got friends in the area? Get them to buy stuff for you and ask for local discount, failing that, haggle, a driving licence with a cornwall address on it was gettig us ~20% off or free wax, flip flops etc in loads of places.
Other things to do in Cornwall (its a quiet place)-
£1 a drink night in the Corn exchange, Cambourne (not recomended if you have a missus)
The Milk challenge (6 pints, 1 hour, lots of vomit)
The drowning game (involves a hosepipe and avoids sore throats after a days surfing, apparenly)
Removing the screws from anyones bed who appears to be about to get lucky.