It seems to be more of a common problem on the passenger side. If the bubbled / rust is not bad it can easily be done very cheap. I think one of the problems is the windscreen rubber seems a little short on the corners.
A friend has just done mine with a spray can (over 30yrs in the trade) and done a fantastic job, I had a 6" long area with only a tiny amount of rust, I could get to it all easily by removing the w/rubber. It doesnt need the w/screen removing unless the rust has kicked in which you can only tell by rubbing it down.
Mine cost £26 new porsche w/seal, £8 approx paint mixed, £8 for laquer and another £10 for sandpaper and undercoat.
A good man in a van could do it easily but thr problem is if the paint does not match it looks awful, but lucky mine was spot on.
The way I looked at it was the job wasnt costing the earth and would protect it for now and I would get it sprayed later if needed (window out), but its done a great job and is near 100 spot on. Unfortunatley hes just a friend and no longer does spray work so I cant recomend anyone. But it should be £200 max if you can get by with keeping the window in.
I know a spray can sounds dodgy but I have seen bonets done with them before to the highest standard (its just what your used to working with). I know theres a chap who is supposed to be spot on in nottingham who does all Grey Pauls Ferraris, from what I have heard hes quite cheap as well (but I have been waitng for his number for a while) someone else might know of him.
Im in Leicester so you can see the job if your every passing.