The bolt has to be headspace to the barrel. Its not a size or series issue. It literally is a unique fitment. Now, $500 is asinine. The bolt should run you a couple hundred. Headspacing by a gunsmith should run you another $100-200.
A quick check shows a magnum bolt face bolt with ejector and extractor, firing pin, spring, and cocking piece all in stock at Numrich. Buy the parts and build a bolt, then take your rifle to a gunsmith for headspacing. Don't skip that last step. Seriously.