How much?
Really depends.... ordered a BZ250 which is the lowest priced MPPT that I know of, ignoring fake ones on EBay, is roughly 125 to 150 US$. A step up in my opinion is the Blue Sky.. for roughly 220$
But.. these are pretty much limited to 12v Battery Bank... Although the BZ... has a solar top end this it much higher than the Blue Sky.
End of the day, I prefer the Blue Sky... better construction.. the BZ can be a bit flaky.
BUT.... If you are thinking of growing into the 400W+ realm.... there are a ton of better choices.... don't plop down $$$ for something you will replace in a year or 2 as you out grow the controller...
I have done this.. I have a Blue Sky and and A BZ... both are being replaced by a couple of Morning Star TS 45 MPPT. There are also other mppt vendors.. but I like the the first TS 45 I bought.. so that's my plug.
Rover