a 1000 gal custom tank is going to be near 8-10k. easily. 10x4x3.5 would probably be the dims give or take, and depending on material and who makes it you are looking at a hefty price tag for a brand new custom. I'd be super cautious about having your LFS make you a tank...not that some places probably have some serious tank skills but that isn't their main focus as an LFS and as such you may run into complications with the tank.