Suggest visit the RYA site www.rya.org.uk
then peruse the sites for various of the schools. Prices do vary but then so too does what you get for your money. As a guide we charge £290 (inc VAT) for Level 2, for us this includes Fuel, use of waterproofs (some schools charge), and copies of the RYA Powerboat Logbook & Powerboat Handbook. Schools will vary as to whether their prices include more or less than the above.
As the Nei(a)ls suggest ring the schools, see how they seem like they will satisfy your training needs and go with your gut feel. You might check this link out as it gives a checklist for assessing schools http://www.powerboat-training.co.uk/schools/schools%20-%20choosing.htm
It certainly pays to shop around and get a feel for the various organisations out there, if you are going to spend a reasonable chunk of cash its only reasoanble that you get the best return on that investment