I consider myself a "controlled" TF collector.
I consider myself lucky ... I'm no longer in school and hold a very stable long-term job. So, I have a bigger budget than your average TF collector.
However, I still budget my spending habits when pursuing my hobby. I try not to fall victim to "impulse" buying as much as I can. It also helps to have a wife that keeps an eye on your spending habits too!
For me, the best way to control your TF spending is to focus only on the characters, figures, and lines that you truly like.
I absolutely avoid Animated line, Heros line, and Legends class.
I love Cybertron, Movie, Titanium, Classic, and Universe 2.0. Also, I tend to focus on the deluxe, voyager, and the 3" titaniums.