Pretty sure Coral Gazers sells RODI and RODI/Reef Crystals and RODI/Tropic Marin Pro. I used to go there when I first started out. Never tested the RODI though so i'm not sure if it was 0 TDS or not. Cost was $.49, $.69, and $1.20 respectively.
Amazing Aquariums and Reefs has RODI for $1.00 / Gallon and RODI and I think Brightwell salt for $2.00
Reef Lounge RODI is $.85 and they also have RODI/Coral Life for $1.20 and RODI/Red Sea Coral Pro for $1.60