The $100 I "imagined" is for Gold Phoenix (ultimately the board house BatchPCB uses) which is more like $90 for 100sq in panel. This is double sided, double solder mask, and they route as many boards as you have for free. An extra $30 means you can have up to 6 different designs that they will panelize for you.
I do like gold phoenix (and I do a few designs at once to keep costs down) but I know that's not for everyone which is why I didn't mention it (and brought up olimex which I haven't used for a while).
I wonder if there would be any interest in a group buy. 155 square inches for $140 (with the $30 extra). Divided 6 ways is $24 per person, and that would get each person about 3 shield-sized boards. Throw in shipping to north america and then to the individual buyers and you're looking at about $30 a person.