The x-valve with ULT works very well, but not much tinkering after you get it set up.
A pneu may not be cheaper, depending on your existing parts and plan. Pneu'd classics tend to chuff a little more than the x-valves as you push yourself on the trigger. Building a classic pneu still allows you to add an x-valve later, and it's a lot of tinkering.
You can also take the usual maggot path, one or more of each.