They are pulling the cover over your eyes!

No way is that £1,500 to fix. the bushes are a couple of quid each as is the brake hose and the CV boots/gaitors.... Thats half of the project done.

I'm sure a steering rack is about £30 of ebay.

The other bits can be had from breakers on ebay, theres plenty of XRs being broken on there. I reckon £300 in parts alone. So they are charging you £1,200 in labour.

Find another garage or do 75% of the work yourself a novice can do that stuff. The tracking a garage will do, at the same time fit the steering rack and fit the gearbox.

The garage may be able to weld a new exhaust mount(if its on the chassis) or it'll be replaced with the new exhaust you'll be buying.

Post a pic of the rotten door, it may need a little bit of welding or again replaced from a breaker. If the door has to be replaced it'll be about £100-£200 cash job for a respray.