Co2 controller

So I grabbed a tank of co2 and a titan regulator.
i was thinking about grabbing a controller to help me keep my ppms around 1200-1500.
possibly when it hits that target ppm, it shuts off.
then when it falls below, kicks it on.
Any suggestions? Possibly around 300$ is my budget for it.

I picked up one of these.. Only $210, but I have a tent, not a room to control. I didn't need bullet proof, just functional.