If your goal is to be adding calcium and alkalinity into the tank using a calcium reactor, I would say $400 is relatively cheap. My setup is:
Wow that adds up quick
Vertex Reactor - $500
10 lb cO2 tank - $100 (can go for a 5lb tank for a little less, but worth the upgrade I think)
cO2 in the tank - $30
Carbon Doser cO2 regulator - $300 (can get a cheaper regulator at $125, but harder to dial in)
Masterflex Peristaltic feed pump - $250 (can feed off your return pump for $0, just harder to dial in)
44 lb box of TLF reborn - $100
If you are looking for cheaper alternatives to add Calcium/Alkalinity, there is always 2-part dosing or kalkwasser. Depending on your dosing requirements, they are much cheaper alternatives that work. Calcium reactors are a lot more $ up front, but add the benefit of being more set it and forget it, as well as adding back trace elements and not just the big 3.