I paid neck end of £500 for Pentagon Supaglass on all side windows, and tints on the rears and back of the Bora. I could've done a better job with one hand and a plastering float. Professional tinting is a little different to paying a professional to tint your car. It cost me good money to put right the damage they did to the trim, and the actual tint job was dismal aswell. Dirt under the film, bubbles all round the rear windscreen, scratches on the face of the film where it was bonded to the glass.
If you're going to have tinting done, take a look at their workmanship before you let them lose on the car, and check the work before handing over any money.