I tinted the rear lights on my 320 with....... dont laugh now....
womans tights!
just remove the rear clusters and stretch the tights over them. secure it and bolt them back on. It sounds stupid but it works and you really dont notice that it is tights.
The effect is not as strong as from say using tint spray but it does look better than standard and costs next to nothing!
heres some pics of before and after - please ignore the state of the car i only got it a few weeks ago and it still needs a lot of work!
hope that helps