Do you reload? Revolver ammo is generally more expensive than 9mm. 9mm can be had for cheaper than it costs to reload it (unless you're casting your own lead). If you reload, there is almost no difference in price between .357 mag and .38 special loads, whereas factory .357 is about 1.5-2x the price of factory .38 (completely arbitrary). I load all my hot and cold loads in .357 brass to avoid the carbon ring at the .38 special case mouth in the chamber (as also I do with my .44 mag).
A revolver allows you to play around with your loads more than a semi-auto, because you don't have to worry about having enough power to cycle a slide. I have a hollow-base wadcutter target load that barely recoils more than a .22, for example. You can certainly load warm to hot for a semi-auto as well, but you're limited as to how much you can cool your loads.
On the flip side of all this, a revolver is much more time-consuming to clean up after a range visit than a semi-auto pistol. The soot gets EVERYWHERE, and you now have 6 chambers to swab out, a cylinder to clean up (inside and out), a barrel, and anywhere else the frame caught some fouling. With a semi, you strip the slide, pull out the barrel, swab it out, and you're pretty much done other than lightly wiping down the outside, mostly around the muzzle area.
