Smails.. you can win credits in a free tourney. You do not have to pay to upgrade your clubs.
I can't speak for most people, but I can tell you what I, and some friends I have been talking to, have done. After playing the game awhile, we decided that it was worth sending WGT a $20 or so to upgrade the clubs.... I would like to say that it was mainly because of the 'shareware' feel of the game, you know.. play awhile nad send a couple dollars if you like the program to keep the programmers working on it... but it was more that we wanted the extra couple yards on the clubs. lol
Either way, the choice is yours. You can play the free game with the free clubs as long as you want. You can upgrade at anytime, too. If you win some free tourneys, you get credits.
But, having said all that, I just look over and see that credits are 1¢ each (or 2 for 1¢ if you use AmEx) and realize that it's really not that expensive for all the hours I have been here.
Hope this helps. Good luck!!