NEED ADVICE :( RUST!!!

Hello to you all,

I've got a problem, and it's really not good. I have found rust on my car,
and it looks pretty bad. The car is an E36 coupe 1996 328 is. I have found
it all at the rear of the car, and never noticed it before, as it's well
hidden.

First area, is between the rear bumper and bodywork. Best way to describe
it is the gap between the bumper and body of the car at the back, but only
along the sides. If you run your finger along that gap you can feel that
there is a roughness to it that seems to be rust when you look closely. I
have been quoted £200 to do that work.

The problem is there is more! This is a lot worse though, I'm amazed I
never noticed it before.. But.. if you open the boot and remove the LH rear
light cover. Twisting the release and then pulling off the black plastic,
as if you were changing a bulb, there is quite a lot of rust inside there,
and it looks like it's gone through! The point I can best describe it at
is, if you imagine looking at the rear light from the back, if you open the
boot and look at that light.. and to the immediate right of it, between the
black plastic of the light and the boot seal, you can see where it's gone
through. It's worse from the back of the light, a lot of flaking.

Now in one sense it's not so bad since you can't see if from outside or even
in the boot with all the plastic covering, so really I don't need it
spraying, I just want it repairing. I've had all the light out, and the
boot trip and it's not spread in either direction. I was very thorough in
my examination, had all the carpets out etc.. This is the only area.

I have no idea what is involved with this kind of work, and would like some
suggestions if that's possible.. Excuse the long post.. Thankyou

Craig