We bought a house 10 years ago

that had one already–and had a friend put one in his place, about $1000 about 5 years ago. Where did you get the $4000 figure?
Our grocery store sells filtered water–you can bring your empty jug and fill it up–triple filtered, including a reverse osmosis filter. I must admit it tastes way better than carbon filtered water. Carbon filters and reverse osmosis filters are completely different. I don’t think one can compare them–reverse osmosis are probably superior, but wasteful of water and considerably more expensive. I don’t know of any BRTC that sells them.