Cheapest way out would be a Perfecto 265, 84"L x 24"W x 27" or 28"H. Best bang for the buck would be a Perfect Deep Series 300 72"L x 36"W x 28"H. Off the shelf glass will always cost a lot less than custom. But the shipping will kill you on either. Where are you located?
I've got a 225 plexiglass aquarium for sale. It weighs a lot less than a glass tank. It's made by TruVu Aquarium and it's made of 1/2 inch plexiglass and it still weighs close to 400 lbs. I can bubble wrap it and put it on a pallet for shipping. If interested, pm me with email address and I can send you some pics.