Wanting to build a 'platform' sub enclosure. Serious noob. Medium budget.

I'm in the process of finishing my basement, and we are building a home theatre area into the mix. It will be approximately 900 sq. ft. (32'x28') of open area.

My 'idea' is to have a raised platform for one of the viewing couches, and I was thinking the platform would make a great area for a large sub enclosure.

One of the thoughts was to use a pair ( or 4? ) 8" drivers. I have been looking into the large enclosures, reading about tapped horns, and all kinds of other goodies. In my younger days I used to build car audio boxes (sealed and ported) but that was about 12 years ago. Very comfortable making boxes. I'm wanting to get back into it on the home audio side now, just for my own enjoyment. I enjoy tweaking designs, and I have a blank canvas at this point to build in.

My budget is in the $500-$750 range for subs and amp, wood I can get for almost nothing (I have connections). Already have a receiver I like to drive the other channels for 7.1 sound.

I was looking at the Tang 8" subs from parts express, but wasn't sure if there was a more efficient / better option at a similar price point.

Ok, have fun chewing up my idea. Serious newbie here, just looking for ideas.

CJax

My thought on the smaller driver was that I am going to need to keep this 'hidden' as the wife doesn't want to see them. If I can build them into the cabinet and hide them that way it's helpful. I'd love to do 15"ers but I don't know how well a down-firing build would work in a large enclosure like this.
Am I off-base with this design plan? Also, wouldn't the larger drivers require a little more $$ and a larger amp? Again, trying to keep the budget realistic.

Thanks for all of the responses!

For starters, I have 9.5' ceilings, so I was thinking a riser in the rear sofa section would be optimal This will actually be in the center of the room.
As it's going to be laid out, the front and rear are 28' walls, and the sides will be 32'. Along the front 28' wall will be the projector screen. Along the back wall will be a wet bar / full kitchen area. I was planning on having my electronics along the left side wall to keep the front area more open and less distracting during viewing. Also makes it nice when we decide to have parties.
I'l have to get a pic up to describe this better.

My reasoning for the 8"ers was to keep the platform down to a single step if possible. I am all for a good horn build, as floor space is not an issue.
Another thought was to possibly build 2, putting one on each side of the room, standing vertical.

FUN4ME, I like that design idea. Considering 2 of those at the moment.

BeerParty, I know what you mean about space. We lived small for quite a while.
This place was our dream house. We built huge 6 years ago, but the inside was very unfinished. Easier to put up a SOLID exterior and structure, then finish everything inside with cash, than to have a huge mortgage on a puny finished house we hated. We are now in finishing stages on a cash only basis. I was lucky to squeeze this into the budget. The little lady was very generous on this one. We have finished everything but the 1800sq.ft. basement to this point. Now it's all framed in, just waiting for the HVAC and drywall to get done. Added 3 bedrooms, a workout room, a utility room, and a full bath, plus the entertainment room.

on the thought of the 12"ers, is there a good horn design (I still like the riser idea) that utilizes them in an up/down firing position/? The price point sure looks right for what I'm doing.

Thanks again everyone. Wish I'd found this place long ago. I''d probably be knee deep in toys at this point.