I just bumped into this over on the DIYaudio forums. I haven’t tried it but they seem very cheap:
Ok, this looks cheap and good. I’d have to try it 
Very good find!
This may be worth checking out. They do it in three’s typically so may not be ideal for boards you know you will only need one of but otherwise it is $5 per sq. in. for 3 boards. Not bad and, though I haven’t used them myself yet, they have been recommended both here on these forums and from my local hardware group.
It’s nice to see options other than BatchPCB and Advanced Electronics, among others, for sure!
(Removed and put it in the right place)