There's no way a 12k btu will cost 5k... Sorry dude I think someone is trying to bend ya over a barrel on that one. We had 2 large rooms, running x12 1kw DE fixtures in each. Each room had two 32k BTU handlers. The cost was like $2500 each plus $400 +/- to do full install and charge the lines. Thats with no discount on buying four of them, and that's also in CAD funds. If your American that would be half the cost with exchange lol.
Everyone wants to run a big boy room, but don't take into consideration the additional cost and watts of cooling. Unfortunately that's the catch to them... I already posted in another guys thread about something similar bout trying to skip out on the AC. Yeah its doable in the winter but there's variables and you must have a good lung room setup. Don't attempt to duct in that cold air or you'll have a mess of condensation on your hands. That being said if you decide to cheap out then spring comes and fucks shit up, and then summer hits and your shut down completely cause its hotter than Hades. If your a guy only pulling a couple crops during winter than shutting down for summer then ya it'll work so long as you pre-plan.