hate to be contrary... nah, hate's too strong a word<G>...
Priorities for acoustical treatment for a small, critical listening space, to me, would look something like this:
1) select your monitors - use what you go, budget for new, makes no difference.
2) GEOMETRY - trapping LF and reflections is fine and good, but, it's even better if you don't need to. That means focus on geometry, and if you can't move the walls remember you can move the loudspeakers, and your ears! Try to keep the distance from the back of your head to the back wall at least
(roughly) 12 feet - this provides a lot of options further down the road. 3) Bad reflections - there are bad reflections, and not so bad reflections... start with the worst reflections. Even if you just sketch out the room on paper it'll be easy enough to see the bad ones. Adjust the geometry to get rid of them if you can, otherwise treat them.
4) LF problems - I almost always leave these to last because the other steps will usually mitigate them.
A couple other thoughts
- avoid tuned traps, broadband traps are easier to work with, tuned traps should be a last resort.
- avoid tools that claim to correct time domain problems in the frequency domain. I know a lot of people like them, but the fact is you can NOT equalize out a time domain problem yet - the horsepower to create the required information isn't here yet.
- be aware of just how much absorption you are adding to the space. Too much is, well, too much! There are other tools, such as diffusion and reflection, that you want to use as well.
While it is a difficult pill to swallow, allocating some of your budget to work with an acoustician can pay for itself many times over. Even if they just make suggestions, they've dealt with small rooms a lot, and they can provide that experience to help you avoid gaining that experience<G>!