The problem you have with quoting for full resprays on older cars is that there is a good chance of unforseen problems occuring such as rust or previous accident damage that has been repaired, this will always push the price up so you have to expect that when you get a quote, the chances are the finished article will actually be a higher price than orignially quoted.
If you wanted to reduce the costs slightly you could always do as much of the work yourself as you can for instance stripping off panels and trims but then if you break it, you have to fix it. You could also refit it all after but then there is a chance of you damaging the paint
The best thing to do is go to a few bodyshops and have a chat with them and see what you can work out, there is a good write up in practical performance car this month about bodyshops which may prove useful to you
