This a great question for anyone who takes pipe smoking seriously. I have a friend who will buy a pouch of Half and Half and smoke from it for 6 mos. He is never bothered with how much is too much. He smokes a cob until it wears out and then buys another. It is instead a question for many such as frequent pipe boards and who have made pipes their study, in which case they can tell the difference between the quality of factory pipes and an Ashton, between that pipe and the current darling of this board Ryan Alden, and between that pipe and a Doctor's, and finally that pipe and a Geiger.
How much is too much is a great question given that a beater off Ebay that was drilled correctly and had wood of a sufficient cure is going to smoke as good as a Former. But Marty Pulvers has been known to extol the virtues of Ingo Garbe who he calls the "ultimate pipe purist." He had a Garbe pipe that smoked so well that he bought another for top dollar but still hasn't smoked it, afraid that he'll be disappointed. I'm sure the Garbe that he has does smoke better for him, but I've not read anyone who makes such claims put forward any communicable qualities that state why or how this is so. If such difference exists I would think it could be put into language and shared.
I cannot find any difference in smoking qualities in my pipes, and it's taken years to come to these conclusions. Retailers are not shy about singing the praises of the pipes they sell, and the forums are replete with the assertions about pipes, which in my opinion are not true. One pipemaker says that it is the smoothness of the internals that makes a pipe smoke better. To me this is ridiculous as whether the smoke has to navigate a channel that has not been sanded or another with some amount of roughness, to me, just can't impede the flow of the smoke. I don't understand how obstruction of even a quarter of the airway would make much difference. This might slow the smoke a bit, but it's hard to believe that the smoker could tell the difference in the amount of smoke resulting in his mouth, especially if he didn't know about the obstruction.
Pipesmoking is a terribly personal act. In considering it I always come back to the internal questions. What was the mood of the smoker? How much did he actually try to taste the tobacco rather than huffing on the pipe; did he take his time or was he in a hurry? To what extent is his palate developed? How capable is his smoking technique? Finally, what is his attitude about the pipe he is smoking? I think it's much more the case that the answers to these internal questions influence what we taste and how we think the pipe smokes than that some pipes have a special magic. The subjective in pipe smoking is huge.
YMMV. These are just my thoughts.
The simple answers to your question have already been given. Pipes are expensive. Like Mike Glukler said, only buy what you really like. Good luck!