If anyone wants to get these PCB's fabricated extremely cheap JLCPCB (https://jlcpcb.com/ based in Shenzhen) currently has a promotion where they are fabricating PCB's for $2 total, 1 day build time, and with free DHL worldwide shipping. This + $20 BOM (minus arduino boards) makes this project super cheap if you are already comfortable with SMD soldering.
I've gotten other boards from them and haven't had any quality issues, comparable to other shenzhen fab houses like PCBWay. Don't mean to sound like an advertisement, just letting people know.