The price depends on how many tubes you buy. I am selling my kits installed $4000 and up depending on the amount of tubes, holding tank capacity, forced air heating etc. When buying a good rule is ten tubes per person in the house.
i am a newly qualified solar panel installer and in the copper tubes inside the evacuated glass tubes is a single bead of water, if you take a copper tube out you can hear the the bead of water drop to the other end like a metal bb. and dont forget to clean the underside of the tubes every 2 months so get rid of any moss and what not.
Another method Two points of method: (1) Two waters, separated, zero pressure and house pressure, and (2) Use principle of heat-exchange to take heat from zero pressure to house pressure by running copper metal tubing with house pressure, inside the zero pressure water. The copper metal does a very good job of transferring the heat, and many times better than plastic or rubber. Mixing sand and water in the zero pressure water is probably better. Thin aluminum may contain the zero pressure water.