You didn't mention the size of your system, so it's hard to say if what works for my nano reef will work for your needs.
The CPR Tumblers are very affordable (~$40-50 at
Marine Depot). I run the Nano version on my ~20 gallon tank and use Warner Marine's EcoBak biopellets. It keeps them tumbling well and offers enough control on the included pump. I was mostly concerned about size and function, so it fits my needs at a nice price. Been using it for about a year now.
As a drawback, the reactor is not exactly built like a champ. The Nano is tapered towards the bottom and sits on the end of a small powerhead. It never wobbles around, but it has a lean to it and can't be balanced perfectly vertical. Not a big deal to me, since I was just happy to have it fit in a small space of my sump. (The Mini version has suction cups on the side to keep it positioned a little more neatly, but it was larger than I wanted.)
Again, not sure if it's large enough for you. WM EcoBak is 250mL of pellets per 50 gallons of aquarium. I can't speak for the Mini version, but the Nano probably can't handle more than a 30 gallon system. That would change if you found a biopellet media that requires less pellets per gallon, of course. I never really looked into it.