For small quantities and prototypes, OSH Park is great. However, for quantities, it's a horse of a different color.
Take my board...
Detected 2 layer board of 1.92x0.84 inches (48.74x21.44mm). $8.05 for three, that's $2.68/ea.
If I order at least 60 of them, I can get them for $1.68/ea from OSH Park. However, if I go to my Chinese board supplier and buy at least 100 of them, I get them for $120 shipped.
It is nice to know I always have an alternate source of boards if I need it.