The only cheaper route for setting up a car for flat tow is to be able to install it all yourself.
But I agree, don't purchase the items through a dealer. Some dealers will jack up the install price if you don't buy the products through them. But keep looking, you will find someone who will give you a better price. 2 RV dealers gave us prices that were about $1000 more than what we could buy them for ourselves through amazon. Shipping savings was about a 1/4 of that. Since we don't fulltime, we opted to go the tow dolly route. Still saved nearly $1000 off of what we could buy the parts for plus their labor fees. Plus if we change cars (which we are known to do), we won't have any additional cost.