Until just recently if you wanted to make your own d-star repeater at a fraction of the cost, there was one way. That was the Satoshi GMSK node adapter.
To build this adapter the cost about $70 as compared (+ your analog radios) to the cost of a Icom RPC-2 Controller plus a RF band module at about $2900.
As one can imagine the GMSK node adapter is very popular. There are a number of other revised clone boards out there (and gmskhotspot.com) to feed the need and address small board errors in the original design.
The problem being is that there is not always credit due to the base designer and PIC code author Satoshi Yasuda 7M3TJZ/AD6GZ. Currently, the PIC code is in a state of being re-written to satisfy that it doesn't infringe on his rights.
In this impasse Jonathan Naylor G4KLX's sound card based GMSK / D-Star repeater controller project has gained a lot of attention and advancement.