About 4 years ago I bought mine at Guaranty RV, it was cheaper then anywhere else. The price looks like it's gone up, I think I paid ~$190.
FYI, the new coolant tank does not have the same level sensor. The original was mounted on the top, the new one has threaded ports on the side. It takes a Ford sensor, can't remember the part #.
Here is another link to what you will need
Advanced Search
Do a search and see if you can find the sensor #,
I did not buy a wiring harness, just made my own.
Also, you will need 2 each 90 degree pipe fittings for the top, I was able to buy at Lowes but can buy at other places.