What I would recommend is to have the locksmith make your ignition key first, then once it works the switch you can try it out around the car to see what else it fits.
There are a couple of basic ways to fit a key. One method is called 'impressioning' where the locksmith starts with an un-cut key blank and goes through a process to file the correct cuts into it. You don't have to disassemble the lock for this technique. Another way is for the locksmith to pick the lock to the open position to remove it from the ignition switch housing, disassemble it, and file down a key blank to the correct pattern based on the pin sizes inside the lock cylinder. As mentioned earlier, some locksmiths can 'read' the pin heights with their tools without disassembling the lock and cut a key that way.
You can use newer, less expensive blanks for your car, as long as having a more modern key head doesn't bother you. If the locksmith you're talking to gives you a funny look when you use the words 'impressioning', 'reading', or 'picking', do yourself and your car a favor and find another shop.
Harold