If you are wanting to hunt deer with a pistol, I would recommend looking at the many different brands of revolvers available today.
The minimum calibers I would use for deer would be the following:
1. .357 Magnum
2. .44 Magnum
3. .41 Magnum
4. 460 Caliber
5. 500 Caliber
6. 45-70 Caliber
7. 454 Casull
There are some other less-known calibers out there, but these are the most popular. Unfortunately, none of these calibers are very cheap. You can shoot 38 specials out of a 357 mag revolver, and you can shoot 44 special rounds out of a 44 mag revolver (that would save a little money, but not much). Even with these calibers, you need to make sure you are close to the deer to ensure an effective (i.e. humane) one-shot kill.
Research, research, research. The internet is full of useful information. I would also recommend looking around this forum at all of the different topics.