I at least partially agree with most of the advice above. For me, the R11s improved my game at the lower levels more than anything else. Hitting more greens and getting several feet closer with the approaches dropped shots in a hurry. And as a tangent, when it's a tough pin, don't get cute with those beginner clubs; knock it to a safe part of the green.
If the irons are too expensive, I would say keep plugging along and wait til you can get the Ping wedges in the 40 levels. Putting is huge, but I don't think those super cheap putters help out a lot. Wait at least until the Ghost Spider at level 35.
And here's one of my thoughts about clubs that I think is in the minority yet again--a great driver is worth more than probably anything. The Taylor Made Driver at Level 48 is expensive, but it's a dream. I bet I instantly dropped four strokes a round with that one club.
Good luck.