I paid $1000 for my 500 gal and the moving costs were also another $1000. I feel your pain.
If you shop smart and are willing to put in the work, you can get it at $1 per gallon. The question is moving that beast.
I agree with Pufferpunk. She knows her stuff. Get what you can, and enjoy it. Accept those limitations. Once you step outside that boundary, you're asking for trouble; both for yourself and the fish.
Keep it simple to start and graduate to bigger and better.
I think that's a very good Christmas gift to give him! As long as you are sure the store knows his housing requirements & will only sell to someone who is prepared to house him in a very large tank. What sized tank do they have for him?