Well, they do have a version of what you are asking about at DFRobot… for example a qty 10 of their 2 layer 10cm x 10cm boards is $23 (plus options and shipping). They also have a PCB Copy dropbox where you can select 2 copies in 1 PCB (+$15) and 3 copies in 1 PCB (+$30).
So this means if you could fit 3 of your boards in a 10cm x 10cm area, you could get 30 PCBs made for $53.90, plus options and shipping. I’m not sure I understand fully, but I think you just provide the gerbers for one copy and they fit 3 into the space themselves… but I’d email them on that one or maybe someone else here will know.
I had a great experience on my order, and Justin from the forums gave me a bunch of help on the ins and outs of DFRobot. You can check out the thread where I got help here: https://www.ghielectronics.com/community/forum/topic?id=11673