Infinity vs Dayton Titanic
I've assembled a couple of subs using older Infinity Perfect 12" subwoofers and Dayton Titanic MKIII subs. I first started out with sealed 3 cubic foot boxes but I eventually ended up porting them for the significant increase in clean output.
I'm far from an expert but here's what I noted in my builds.
One, I really like the Parts Express subwoofer enclosures, especially the black vinyl as they are easy to customize, look clean and hide well in the room. That said, 3 cubic ft is still pretty big.
Two, for whatever reason, my infinitys seem to have greater clean output and break up less under serious stress. You can pick up an Infinity 120.09W 12" sub which looks quite similar to the older Perfects for about $130 at amazon (and other places).
Three, porting either sub in a 3 cubic foot enclosure works great without sacrificing a nice response curve. I used WinISD and for both of those drivers, I typically ended up using two 2" flared ports running approx 11" long (if I remember correctly). You would have to model it with whatever drivers you actually went with.
In summary, with your budget, I would build just one box with the Infinity 120.09W sub, two 2" Precision Ports, some binding posts, polyfill, etc. I think you would be really happy with the end result. I will say that my Infinitys can certainly demand amp power but they also seem to handle it well.
Of course, if you are a better woodworker than myself, you could certainly build your own sub box and save some cash.
good luck!!
Jotham
P.S. Re-reading all the preceding posts I realize that I went off topic a lot. What I was trying to say is that pound for pound, I've had a better experience with infinity subs in very similar builds. I would (and have) build at least two separate enclosures with infinity subs and not use a Dayton MKIII. Infinity subs behave very well sealed but I feel that a mild porting has all benefit with no downside (that I can hear).