You could build one for less than 10g's if you have the skill and you can meet or surpass codes. Lumber, concrete, misc. screen, roof, does it need a pad? Couple friends for a small amount of time, most you could do yourself. 3-5g's without pad 5-6 with. I would think footings for 4 pretty hefty posts would be required. Might want it bigger with 6-8 posts? Could go over 6-8g's. It would be nice though. I would think seriously about location. It's going to be kinda permanent.