heres my .02 for this.
If you can't afford to build this tank correctly without cutting corners, you certainly won't be able to afford the clean up of all the water on your floor when the tank explodes.
I am not complaining, I just flat out don't have money.You are planning a 12x2.5x3 tank and are complaining about $1000. I am planning a 10x4x30in tank and am struggling to keep it under the budget of $8,000-$10,000. Even if I was go to plywood, it would still be $5,000-7,000 probably.
I can cut up my 90 and get four panels (2x 4' and 2x 1.5') of 1/2"+ glass. I would use that marine vinyl to seal a box and stand of wood (I intend to buy a roll anyway to build a greenhouse and a canoe) that I already have and coat it with deck sealant keep it from rotting(I already have that too) and use one 3200gph powerhead to run a pvc canister filter made of 6" diameter pvc and a pair of big plastic tool boxes. I know this will work as I someone on DIY Fishkeepers built a canister filter using a bladed powerhead got 3/4 of the rated gph out it, plus they draw only 18w. Lighting would from a window and some cheap LED strips my father bought to light the living room but my mother wouldn't let him install because she didn't like the look. The top lid would be 1/4" acrylic, so I could use the room's lighting also. Plants would be form a local lake and do part of my filtration, maybe even with some emergent growing through holes in the lid. How's that?Here's a Idea find a cheap 150 or 180 and viola you have two 72" viewing panels
I understand what he's saying and, in theory, it could work, but I strongly advise against it.