IF your looking for a Hi Point, figure $200 out the door with an extra magazine.
If your looking for a Glock, Figure $600 give or take depending on your area.
If your looking for some of the Sig's or H&K's better take a grand.
Now for the Revolvers.
If your looking at a Charter Arms, figure around $300
If your looking for a Taurus, figure $300 to $500
If your looking for a S&W or Colt figure $700
Their is a very wide margin in price, quality, and availability of a gun. Then new or used will also determine a value and the supply in your area. It's very difficult to say a value on a range of fire arms.
Brands to avoid no matter the cost will be Jennings, Phoenix, Jermandez or how ever they spell that, and basically any other brand you don't resonize.
Good brands will be
Hi Point ( Lowest quality but "Best" quality of the junk guns )
Charter Arms ( Lower quality then other )
Taurus ( Good quality, low fit and finish, better revolvers then Autos )
Smith and Wesson ( Good all around )
Glock ( Good all around )
Springfield ( Good all around, XD series auto's are nice )
Beretta ( Good all around, the 92 series is the side arm of the Army )
H&K ( Great, but can be finicky on ammo, starting to get expensive )
Sig ( Great, Special Forces use Sigs in the U.S. Military. Expensive )
Their are others but I can't think of them. My best advice will be to go to a local gun and pawn store, or a regular gun store like a Cabellas, Bass Pro, ect. Look at the prices in the case, a gun show price should be lower then a main gun store since your buying from what would be like a gun Farmers Market. Talk to the guys especially at a pawn shop. Ask what they recommend because if you buy a gun from them and it's not working right guess who pays shipping back to the factory? My pawn shop I shop at pays shipping to get a gun fixed, so they are more then happy to say what's garbage and what's not being brought back with issues.
Now my personal preference. Smith and Wesson M&P Series, I like the Compact version better myself but any of them are good. I own 2 and love them both. Very reliable and you can switch back straps out on the grip to make it fit your hand better. For a Revolver I have a lot of experience with Taurus and can recommend them. They are not hi end by any means but very functional. I have a Taurus 85 sitting on my hip as I'm typing this now, a 5 shot Snub Nose loaded with Federal +p Hollow Points. Had it since 2006 and I trust my life to it about a quarter of the times I carry a CCW. Sam can be said for the S&W I mentioned.