You have been able to build more than 20 milliwatt hotspots and repeaters for quite a while.

https://sadigitalradio.com/digital-radio-how-tos/make-mmdvm-digital-repeater/
http://digiham.boards.net/thread/13/dmr-repeater

The interface is Arduino based. Originally there was one source from Bruce Given VE2GZI.

Here are the derivatives that I know of:

http://www.inadvm.com/inadvm/inadvm-rev2-index.html

http://www.repeater-builder.com/products/stm32-dvm.html

http://www.micro-node.com/store/#!/TEENSY-Multi-Mode-Digital-Voice-Modem-Designed-for-MMDVM-Open-Source-Firmware-Compatibility/p/83099252/category=0