MIMF

I realize that every piece of wood in a guitar is important, but where would money be best spent to maximize sound quality?
I am thinking the top, since it what vibrates and everything else is mostly structural.
Of course the build also has a lot do with it too.

The soundboard is the most important piece of wood in my opinion, but it is not necessary to spend a lot of money for it. The more expensive "Master grade" tops may be no better structurally than some 3A or 2A tops. Cosmetics often play a large part in determining the "Grade" of a soundboard.
My advice would be to not spend a lot for any part of the guitar, but buy good quality timber from reputable dealers.

IMO, I'm not sure I've found a correlation between $$ and sound. The higher the cosmetics and appearance (and maybe rarity) of the wood, the higher the price. But not the tone. Just buy structurally correct wood, well quartered, with the least run-out and save the $$ for something else.
If you are asking 'what piece contributes most toward tone' on an acoustic, most people would answer the top, but again, this has isn't a "the more I pay, the better I get" situation. My answer to this question is the top probably plays a stronger role, but every piece of wood on the guitar contributes.

Looks like what I was going to say has already been covered. . .

It's much more to do with how you use it rather than how much you spend on it.

Lots of good sounding instruments have been made from reclaimed wood that has been saved from a dumpster. Whether you like the aesthetic is a different matter...

I've made it a point NOT to buy "instrument" wood, but I have some compulsive tendencies towards gratuitous DIY. It depends on your goals, though. If your goal is to build very traditional Martin-esque instruments for very traditional-minded buyers, then you know what you need to do. If you're just building for yourself/friends/family and want to make non-traditional or found/recycled woods a feature, then I can tell you that the search for your materials can become a thrilling pursuit in itself.

If new to building, buy tops and back/side sets for a couple instruments...your tastes will likely change over time, and few things are less useful than wood that you really don't want to build with, but is too good to toss or donate. The exception is red, sitka, and Lutz bracewood and mahogany neck blanks...I buy as much good material as I can afford when I see it - always useful.

I'm an amateur builder, and have been building 1 or 2 guitars a year for the last 15 years.
I buy my tops from tonewood suppliers, and most are pretty clear that the difference between AA and AAAA grade is purely cosmetic.
I usually go for the AAA grade.
All the other wood comes from various local dealers, I resaw my own backs and sides.

Thanks for the feedback which seems to be unanimous in that price doesn't translate to good sound.
What I have noticed in looking at a lot of EIR back and sides is the more expensive (around $125 - $150) wood has closer, even and straighter grain to it and the lower cost (around $60 - $80) has areas usually on the outsides where the grain gets pretty wide indicating that it is not that well quarter sawn and also sometimes knots. Given the time and money investment in tools I will be making I can't see trying to save $50 on the back and sides for wood that won't look as good and might not sound as good. OTOH I won't be chasing master grade wood that costs more than this.

Again, as Trevor said, sound is much more in what you do with it than in the wood itself. Part of the trick is in knowing what's likely to work with a given piece: if the top wood is not very well quartered and lacks cross grain stiffness, it will generally work better on a narrower guitar, for example. I use denser top wood on steel string guitars, where it confers some useful headroom, and save the less dense stuff for Classicals, where the lower weight can help responsiveness and trebles. Note that you can't go entirely by species in this; there's lots of variation within every species, and lots of overlap between them.

Joel, make some guitars. That will give you hands on experience and judgement to be applied to selecting future materials and designs. Just by making your first and second instruments you will have built a significant accumulation of knowledge. You need and will rely on this experience to make the many decisions that occur in the process of making a guitar. It takes practice, much like painting a picture. If you want to make a "masterpiece" it will require familiarity with the materials and process. Make some guitars.