Hi Goldenboy,
If you're anywhere near Southampton, I can recommend South Coast Tints.
I used them last week (for a mk4 golf), I was able to get 40% off in total so a very reasonable price. Job was well done too.
Just done a online quote for a 3dr mk5 golf (rear only), online price was £199.75, this includes a 10% online discount.
Testing my maths skills here... price without the 10% off must be around £220, 40% off that, makes it potentially around £132!
They had 3 levels of tint, light, medium, dark. He didn't say what % they were. He looked at the factory tinted windows on my ed30 and reckons it's between light and medium.
Apparently law has changed recently for front window tints, they cannot make them any darker, all they can do is put a UV film on the front windows which protects from UV obviously and gives them a bit of a shiny look... if you like that kind of thing...