I have printed single sheets at Costco,
My PicTales and
Scrapping Simply. My PicTales is probably one of the cheaper options out there - 50 cents for 8x8 and $1.00 for 12x12; however, their process isn't a true photo printing process, so the prints are not as crisp and clear as a photo print is, and are a little bit grainy. Their paper was really nice and heavy though, and the graininess (?) on the photos wasn't as noticeable once I put them in album sheet protectors. But I think unless you're not picky, you would be able to notice that the photos aren't quite crisp.
I then tried Scrapping Simply, and was very happy with it. They are a photo lab and print on the Fuji Crystal Archive paper (my Costco prints were on the same paper). My 12x12s were just $1.99 each, but they also print 8x8 at $.99. They turned out perfectly. If I remember correctly, they had a standard shipping charge (like $5.00 or so), and I had my prints just a few days after I ordered.
I don't think I've ever heard anything bad about scrapbook pictures either.
I'm finding that the 12x12 albums get a little bulky (and I'm only on my second album), so I think I'm going to be looking at printing books instead. It seems like a number of people have had good success with Viovio, so I may try them.