You cannot disable it at current. You can change the brick cost in the RTB pref manager, Brick Cost per Volume. 1 means $0.10, up to I think I capped it at 5 so $0.50 for a 1x1F. Also, you need to be an admin to use the full bank - I unfortunately just realized that it will only apply that value when you leave the game or spawn as an admin. I'll fix that in a moment.
Fixed it. It now uses the brickgroup's client to check adminship, if they're online, and the brickgroup's saved value if they're not.