Ammo costs are not negligible . . .
There's also the cost of (practice) ammo to consider -- I don't consider myself any more than an average shot, and I burn through 300-400 rounds of (9mm) ammo per month. The cheapest .500 ammo I've seen is about $30.00 per box of 20; if I were practicing at this rate with a S&W 500, I would be spending $450 - $600 per month just on practice ammo (the cost of a fairly good gun). And for myself, anyway, I'd need significantly more practice shooting to get good with a 500 than with my 9mm . . .