Had a look at the PRs on that site Jeff. There is a Dayton 10" which would do the trick, but it's VAS is still not much more than the enclosure size you are planning on.
However i reckon the 12" might be a good one
The thing is though is this, it has a pretty low resonance frequency so you may find that you simply won't be able to get the thing to resonate at a high enough frequency.
However if you use 2 of these 10" daytons in each enclosure i reckon you'll get the resonance frequency up above where you want it & can then add mass to tune it lower. Also using 2 of them the combined VAS will be much higher & the enclosure air volume will predominate much more, rather than the suspensions of the PRs.
Two of these is still way cheaper than one of those things you were originally linking to