Don't get the cart in front of the horse. Identify what level of precision, over what distance, conditions, lifespan, reliability, how true the parts need to be, etc. Then, "budget" is the lowest cost (or best value) that meets that spec. You can buy a decent-ish barrel and mate it to whatever other parts and shoot good groups for awhile. An awful lot of junk will shoot MOA or better, but not be worth owning.