The best deal I have found on Jet dry is after Christmas, when Target sets up the "club sized" shopping area. They often have a 3-pack of large bottles which are buy two, get one free. I bought a pack each of the last two years when the club sized items went on clearance for less than $7 for 3 bottles. They often will clearance similar 3-packs of finish detergent, although last year I only saw the power ball tabs and gel pacs, not Quantum as I bought the previous year.
I use very little rinse aid, as I have the dispenser set to the lowest setting. I end up adding it a couple of times a year.