72 dpi is typical for most LCD/CRT displays. For print there is no hard and fast rule for the dpi count, and it depends heavily on the type of image and how far away the viewer is when viewing. Most foto printers will produce at least 300x300 dpi and that produces good results when a suitable image is used.

Newer high rez printers can produce up to 2400x2400 dpi. You can also buy software now a days that do a fine job of up-rezzing digital images (increase the dpi of the base image).

A key element is the type of base digital image file you use and ideally you would print with a 16-bit image such as a .tif or a photoshop .psd image file. 8-bit images, which are typical of .jpg and .bmp images don’t have a lot of color/tone gradients and they tend to look crappy. Some jpg images are set in the camera at 72 dpi and that’s okay for al little print, like a 5” x 7” or something but produces terrible results with 3’ x 5’ or even 1/4 of that.

I agree that a 10 mega-pixel sensor based camera will be minimally okay for 3’ x 5’ size, but a higher mega-pixel count sensor is better. Also use a camera that produces so-called RAW images and use some software to convert the images to 300 dpi .tiff or .psd or similar.

You can get some pretty awesome cameras now-a-days for not a lot of money from pawn shops and camera stores which sell used cameras. Go to a nearby store that sells used equipment and tell them what you're trying to do. Many permit you to buy and test.