Well I've just received an offer from York Photo for some free prints (excluding shipping of course). I mention this because they come in at a way lower price per print of 10 cents compared to Snapfish and Photoworks who are 12 and 15 cents respectively.
York Photo, however, are using a standard mail order pricing trick that most of you should be able to see through. They are shifting the cost to the shipping which much higher. Their competitive price comparison chart shows costs against CVS.com, Shutterfly, and Kodak Gallery and uses a sample of 40 photos which will push up the latter(s) costs and make York Photo look better by comparison.
There is, of course, nothing wrong with doing this because every company does it and needs to do it in order to survive. I merely point this out to you to help you when comparing the offers.
I do, however, find it frustrating when trying to compare prices online that you can often not find the shipping cost until you've entered all your details and arrived at the final check-out page. This almost always involves giving away your email address and the subsequent consequences of junk mail and often your credit card details.