Kubiast,
For a low cost reliable weapon I would suggest a Makarov type pistol. You can typically get this weapon anywhere between the $100-300 dollar range. These weapons are extremely reliable and durable. Caliber choices are .380 Auto or 9x18. You can find ammo for either type, but I would prefer .380 Auto, which you can find in any Walmart or sporting goods store. Both calibers can meet or exceed .38 special loadings depending on bullet choice.
Lightweight revolvers are a popular choice, but unless you are willing to practice with them, the chances of you hitting your target is unlikely, especially in a high stress situation. This is true with any weapon, but even more so with the ultra lightweight revolvers that have heavy recoil, especially more noticeable to smaller users.
Unless you are willing to make dress modifications, especially in the summer, I would suggest that you carry in a fanny pack or specially designed fanny pack type holster. I use a cheap 15 dollar pack for days when I just don't feel like strapping a pistol on and for days when you can't...like going to the beach and you still want to be armed.
Good Shooting,
Red