I would still go for the Hydrofarm now. It will be much better than a dimmer.
Then start saving your pennies for an upgrade. You could get a Johnson/Ranco, but they're really not that much different unless you need to control high wattage (which you don't), so the next step up is a proportional. Then you'll have the Hydrofarm as an extra, it's always good to have extra supplies around.

I'm sure someone will jump on in defense of Johnson/Ranco. Every thermostat thread seems to open that can of worms.