I've bought a number of GlocK barrels from Lone Wolf. They weren't threaded. But I believe they do sell them. Brownell's sells barrels also.
Price wise none of the ones I've seen sold, would be considered reasonable.
Your wanting.a specialized quality aftermarket product. It will cost more, that the standard barrel. The threads have to be machined correctly, to be aligned with the bore axis. If a suppressor is mounted. Very bad things will happen, if it sits cockeyed on the barrel. Like the bullet hitting the internal baffles.