Are you going to have a smith do it or try to rent the stuff and do it yourself? If you're going to hire a gunsmith, it might be worth the extra couple hundred dollars to buy top end cut rifled blank. If you're trying to do it on as much of a budget as possible, I understand.
Also, if working with a 243 chamber, it technically needs set back one thread to get the correct crush fit on regular 243 brass. If you are thinking about hand reaming to 243AI, you can jam bullets to fireform, you will just end up potentially having extra headspace on regular 243 ammo.