In my opinion, one should buy the best instrument one can afford. How much one can afford depends not only upon one’s financial situation, but also one’s commitment to the instrument, and one’s priorities. For example, as a professional player, I can ‘afford’ more expensive flutes than I could if I wasn’t a professional, with the same income.
Having ‘good’ flutes are possibly more of a necessity for me than if my livelihood didn’t depend on it. Everyone has to decide for themselves at what price does a flute stop being a necessity. So it really boils down to a personal decision. There is no reason to wait until one is a ‘better’ player before buying a ‘better’ (or more expensive) flute, so far as I can see. A total beginner will still get more from a good flute than a not so good one.
The issue of choosing an instrument is a totally different one, however. The better the flutes, the more difficult it is to determine their strengths and weaknesses. A total beginner will not be able to tell the difference between a $100 flute and a $10,000 flute, at least in terms of playing, much less the difference between a $9000 flute and a $10000 flute, or a $1000 one and a $1500 one, or two flutes priced exactly the same.
I recommend that you buy the best instrument you can afford and that you have a person or persons who you trust (ideally your teacher, or someone that plays like you want to play) help you choose that instrument. Though I could justify buying the most expensive flutes in existence, many of my flutes are quite moderate in price. A more expensive flute is not necessarily a better one, especially after a certain level (US$2000-3000?).
Finally, what makes one flute ‘better’ than another flute, can be subjective after a certain point. The best way to acquire a good flute is usually through a teacher or shakuhachi player that you respect and trust.