batsbrew
before i'd spend money on an acoustician, who will come in and throw money at everything,
i'd bother with building my own 48"x24"x4" deep bass traps, and use those.
Horses for courses, and certainly I took the path of figuring this stuff out for myself, but it isn't for everyone.
Generally speaking (no, I'm not a General) when people ask I always suggest that before spending money on DIY or even commercial solutions I'd hire a studio designer or acoustician.
My logic, for what it's worth, is that any designer or consultant worth their salt can provide a decent solution in a couple of hours. That's maybe $200 - $300 and it saves you a ton of time, as well as money spent on solutions that don't work. That won't be a detailed design, but these folks have worked in hundreds of rooms by the time they get to the point where they are consulting, and they can recognize the obvious problems, and solutions pretty quickly. They also have a wealth of "interesting" solutions from which they can draw.
As I said, I went the other route, specifically because I wanted to learn more. That time was an investment I was more than willing to make. It won't suit everyone.