The 3 bag unit will run $2200-$2300 depending upon whether it's for a 60" or 72".
The initial installation of the hitch for the 3 bag unit can be...........frustrating. The two bag unit for the smaller models is a bit easier to install. Once it's on it's not bad at all to take off and put back on. You need to raise the machine up on jack stands and remove both wheels and tires. The first one I put on didn't go so well but then I decided to actually read the instructions rather than just look at the pictures. I do better with pictures, it helps with may short attention span problem............what were we talking about.
Anyway if it were me I'd have the dealer do the initial installation because most guys won't torque the spindle nut back where it's supposed to be or something won't line up quite right and then they'll be eating belts or something won't be working as well as it could.
My advice would be to have the dealer install it. If you decide to do it yourself make sure youve got a floor jack, jack stands, torque wrench, a little patience and some free time on your hands.