I had quotes upward of $1000. Decided to do it myself. Place it somewhere where it is easy to service. At a minimum, you will need to start it up, clean it once (min) at midpoint of summer and close it down. Pain in the but if 15ft high .
I've done my fair share of servicing swamp cooler. Just afraid that I will install the flashing wrong or drop it while getting it on the roof, so I want a professional to install it.
They are bulky, and kind of difficult to move. Don't blame you for hiring contractor. If I had a good person I would share, but like I said, those I talked too were too expensive for me. Good luck! Cheers!