You can't beat a 226 in my opinion. I have had a 9mm for several years and just got a .357 and a .40 bbl. New pricing is in the $700 range. For used guns, 9 mm's can be found from $400 for well worn police trade-ins on up. If you look around you will probably find a good deal on a used one in .40 or .357. A buddy of mine paid $600 for one in 98% with both barrels. I paid about the same including a holster and some extra 10 rd mags. The deals are out there, especially now as used guns don't sell during the month before Christmas.
As far as .357 vs. .40, I like them both. .40 ammo is cheaper and more widely available. There are more actual street results with .40 if you believe in that school of thought. The .357 has a certain coolness factor to it with the Secret Service carrying it and all, plus it makes a really loud bang
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The easiest solution is to get the barrel for the other caliber - the mags are the same, and for $125 or so it's like getting a second gun.