I think a couple members on here use Costco. I use Wal-mart for my photos. I print them off on the 1-hour machines. 4x6's cost .25 each, 5x7's $1.50 & 8x10's $4.00.
Ryan, with Walmart,it is cheaper to order the photos online than to use the machines. 8x10s are around $3.00, 5x7s are around 60 cents, and the 4x6s are only around 10 cents, if my memory serves me right. It used to be cheaper to order site-to-store, but now all the online prices are about the same. I now use the one-hour service, and sometimes they will actually be ready in less than an hour. The only drawback is that you don't quite have as much control with cropping. If that is a problem you can take that photo out of the order and head to Walmart to use the machine.
If anyone has a Costco or Sam's Club membership, it will obviously be cheaper yet. It's about as cheap as you can get with these two stores. Might even be cheaper to order online and pick them up at the store.
When ordering online they use a diferent type of photo paper to print them of on (Glossy), and it's not the best type they use when going to the store and printing them off on their Matte type paper.
When ordering with the one-hour service online they use what they call "luster" which is a matte finish. If you order site-to-store, you have the option of glossy or luster. I like the matte finish better myself and always use the luster finish.
If you have a Costco membership and their prices are low, go ahead and take advantage of it.
Outside of that, I personally use Snapfish and Adorama. The former has good prices and low shipping, and they're constantly throwing coupons and free credits at you. The latter has cheap 8x10s (a dollar something), but shipping starts high.
I prefer the matte type finish as the Sharpie soaks into the fibers better & quicker. The stuff they put on the Glossy paper to make it shiny fills in the fibers, so the sharpie ink is basically 'floating' on top of the photo. with glossy photos & TTM requests it poses a higher risk of the sharpie smearing when they put it back in the envelope.
I go for Snapfish as well...never thought about matte vs. gloss...maybe I'll give matte a shot sometimes.
2014 Successes:
Tom Baker, Patrick Stewart (vv), Peter Cullen, Robin Atkin Downes, Jenna-Louise Coleman, Trace Beaulieu, George Lowe, Joe Dante, Willem Dafoe, Jeffrey Brown, Maurice LaMarche, Alan Oppenheimer, Penn & Teller (last success 10/14/14)