Godox‘s ReemixÂ RM1 flash / shutter release triggers are now available on eBay from sellers ucolor and Evercolor.
The price is $30 for a set including 1 transmitter, 1 receiver, a sync cord and camera-specific shutter release cable. Extra receivers cost $13-18.
Search keywords: RX1, RM1, RMI
Flash radio trigger comparison guide