IF you want ONLY 4" x 6" prints, the Epson PictureMate is great. Newegg has 2 models now at $135 and $190, depending on how fast you want. They make VERY good prints like pro shops; even though it uses ink jet technology they are waterproof right out of the printer - will not smudge! Can connect to computer, to camera, or to any of many mem cards. There may be cheaper, less fancy models available directly from others, including Epson themselves.
Consumables cost: From Newegg buy the pack of 270 sheets paper plus two non-refillable ink cartridges. At $63.65 with shipping, that comes to 23½¢ per print. You might even buy the 100-sheet packs of just paper (same type), because many find the ink cartridges last longer than the paper in the combo packs, and you can save a bit that way.