Would expect this to clock in somewhere in the neighborhood of $80 using my preferred fab of OSHPark, but their min. order is 3 boards. So if you find two other people who want one, you get one from there for under $30 or so.
You probably can't get one, but ten of them would be around $50.
You're in for a very pleasant surprise once you start looking at suppliers such as PCBWay.com and JLC-PCB.com!
That's what I was quoting, 20cm isn't cheap.
And yet when I fill in the size of that PCB, JLCPCB quotes $11.90 + shipping for 10 PCBs.
Cheapest shipping option is $9.
That's far away from $50...
JLCPCB.com will get a 5-pack to your door for about 20 USD