The Glock 27 comes to mind. When I'm working and depending on where I'm working (some states restrict the number of firearms you can carry), I'll carry 2 in addition to my primary firearm (Glock 23). I like the fact that the maintenance is really simple, minimal parts (34) and the interchangeable magazines. Add the fact that they don't require much maintenance and extremely good rust resistance, and you'll have an extremely dependable and affordable firearm.
Contrary to popular belief, the Glock 27 isn't much more difficult to shoot than your Colt .380 Mustang. Some folks like the night sights, some don't . I like them because it's easier to find my Glock in the dark.

The Crimson Trace laser sight is a great idea for the average citizen for personal protection. The "little red dot" will often be a good signal to the "BG" to move on.

There are many carry methods and numerous products out there. Comfort and concealment are the two primary factors in choosing a carry method. My suggestion though would be to choose a method where your firearm will be "on you". Those "holster purses" for women are nice, but it separates you from your firearm. Mr. Murphy usually hits when he's least desired. When your personal safety is at issue, you want to do what you can to eliminate him from the equation. Whatever method you choose, please be sure to practice, practice and practice. If you can't afford a "blue gun", then you can use the actual firearm. Be sure that it's unloaded and there is no ammunition in the firearm AND no magazine in the firearm. I know a bunch of ladies that get together once a month and have an evening together where they have a potluck dinner and practice their "self-defense" skills. Along with "hand to hand" techniques, they also practice their carry methods and responding to an aggressor.
Hope this helps. Be safe!
gf