I have a two SIGs and bought a .357 barrel for a 40 cal from Bar-Sto. Mine will be ported but a threaded unit costs the same as I recall. I deliberately bought an MT barrel that will require fitting but they do sell what they call "semi drop in". Those may or may not require minor fitting.
I'm no expert but Bar-Sto does have a very good rep for quality. My barrel was $245.00 USD and the fitting could be another $1/200.00.