It depends who you're competing with.
If you are mainly competing with yourself to improve your skills and your tier at the least expense, then I would agree with Lonnie (if you are able to get as far as master on starter clubs - I had to get the old Raptures back in the day in order to reach master when it was the top tier). At some point you are not going to have the firepower to score low enough to keep advancing without shelling out for some decent clubs - long driver, irons with spin and high flight, wedges with spin, and an accurate putter.
But if you are seriously competing now with everyone else, for tournament wins, credits etc., you are at a disadvantage if you are playing against other people (in your own tier or otherwise) who have better equipment, in which case you should upgrade earlier.