[Blarg]

The difference in price in ammo can be notable, especially since the military uses so much 9 mm you can get it as surplus.

45 has much greater stopping power, but has the downside of being more likely to penetrate walls and shoot someone a room or two over or across the street. This can be a significant consideration if you have kids or just don't want to kill the neighbors.

9 mm is easier to shoot because there is less recoil, but the .45's are more fun. There are endless after-market modifications for .45's, too, and plenty of places with a huge amount of experience accurizing them. There's that for 9 mm's as well, but the options for .45's seem endless.

You might want to ask yourself too, what kind of action do you want, single or double? That might figure into what you buy.

Re not spending a huge amount of time practicing, you might want to reconsider. You will probably be much better at self-defense if handling your gun becomes second nature to you. It's hard to afford lots of practice, though, but you can still get in a lot of practice extremely cheaply if you buy a .22 pistol as well. It's great and non-intimidating to learn on .22's. And many are extremely accurate. Fun at the range, awesome to go out "plinking" with in the woods -- set up some cans to shoot, or just shoot at some random rocks or branches, whatever.