It'll be cheaper to just piece it together.
Find a local brewery shop, welders supply, airgas, etc. to price out co2 tanks and what the refills would be. I'd go with a 5lbs cylinder at least just to give you a lot of time between having to refill.
A reliable cheaper regulator/solenoid is an Aquatek premium or you can just look around at reviews for others. I use the Aquatek. I think it was like $90 or $100 on Amazon.
Other than that you'll need a drop checker, I use the cal aqua pearl drop checker which was expensive. You can find different glass ones or plastic ones for under $10 on Amazon or eBay, most come with the indicator solution you need but if they don't you'll need to get the 4dkh solution.
Get a bubble counter, again, depending on the regulator/solenoid you go with it should come with one but you may want to get a more reliable one.
You'll need a diffuser or reactor or however you want to disperse the co2 into the tank.
Get the co2 tubing and some check valves and you should be all set.
I think when I put mine together it cost probably $350-$400, but I went with a 10lbs tank and some more expensive pieces such as my bubble counter and drop checker. You could probably get away with about a $200-$250 complete setup.
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