Sometime soonish we are going to get a cat; we have pretty much decided it will be a siamese or something like that; how much are we likely to have to shell out?
If you rescue a “free to good home” orphan, it’s, ummm…free. 
I may try that first, but it seems unlikely that I’d find an oriental breed offered in such a way; they are very much in demand - in my last house, my next door neighbour’s Siamese cat was stolen from her front garden (they saw someone grab it and jump in a car).
I’ve been looking around the net for you but cat breeders are remarkably coy about displaying prices.
I guess that they don’t standardise the price because you might get one out of a litter that is a potential champion and so is worth a great deal more than the others, in other words breeders seem to assess each cat inidividually.
Prices seem to start at around £50 for a pet, and go up to £600 for show cats/breeding animals, I’ll bet that you can pay a good deal more.
Some breeders will demand that you provide proof after purchase of neutering, and vaccination, and may even want potographs showing the progress of the cat.
Most breeders will expect to see the owner in person too, so buying one as a present for someone else is right out of the question.
These are probably the kinds of breeders you should restrict yourself too, there are a lot of less caring breeders around.
Look at this site for some tips on buying a pedigree cat.
http://www.craigmcfeely.force9.co.uk/Rameses/kittens.html
As for getting a rescue cat, if its a pedigree then you really need to contact the rlevant breed owners club, certain breeds can be very temperamental and may not take well to changes of owners, other breeds are more likely to have certain behavioural traits that can be unwelcome, you need to know what you are dealing with.
I wish you were in the United States. You wouldn’t believe how many Siamese are “up for adoption.” Check out www.siameserescue.org just to give you an idea.