himharps:
First off, I'd suggest not buying the set. You're going to outgrow those clubs quickly. I first upgraded my driver, then irons/putter then wedges. Take advantage of the free credit offers and frequent credit deals. You can upgrade clubs individually as necessary.
I would buy the sets that are made available in the "bundles" that are often made available as you reach different levels. As I recall I got an offer to buy a Ping Bundle somewhere around L79-L80 that included the L81 driver and 3wd and L83 irons. I didn't buy that one but then around L88-L89 I got offered a bundle for the L90 TM Driver and irons and several wedges. These bundles are about a 40% savings over buying the clubs on their own, and can last as long as you need them to.
I'd also disagree on the order of upgrading. If you need the Driver to reach certain fairways or greens in regulation that's fine (and who doesn't like to hit the big drive), but from there I'd go to the best set of wedges you can afford, then a high lofted set of irons, then round out the set with a complementary 3wd and lastly putter. You can go quite far into the game with even the lowly started putter if you learn to read the greens, and it's the one club where distance/spin don't matter. A good set of wedges can save you a lot of strokes per round just by the variety of shots they offer and the ability to get it up/down when you miss (or can't reach) a green.
Free credits may be limited depending on where you are geographically. The double credit weekend TapJoy games offer far and away the best bang for your buck, but depending on where you are located you may not be able to get these offers. (Keep in mind this is limited by state/federal laws and by TapJoy, not by WGT). Also you need an Android device (or PC with Android emulator) in order to get the game offers. Just about everyone with a mobile phone can do the free 2 credit videos, and you can take a shot at the surveys - some have had some luck with these, others not so much.
WGT used to do 3-4 "Free Rental Weekends" per year, and you could pay small rental fee and then get a 25% discount if you purchased at the end of rental period. I can't recall them doing a single one this year though, although maybe I'm forgetting one early in the year.
Basically it comes down to if you REALLY like the game and get some entertainment from it and want to improve at a faster pace, you will probably end up spending some on it just like you do your other entertainment dollars. If you view it as just a way to pass some time and refuse to or can't really afford to spend a little, that's fine too, but it will take you longer to accumulate free credits in order to upgrade.