In the 16/22kW range check here:
Norwall PowerSystems
They have every brand you would want. And below 25kW their prices cant be touched. For example on a 22kW I buy about 5-8% below their sell price. Then because I have nexus in NC I have to charge you sales tax...AT best If I bought it, handled it, processed it, made $0 and sold it and charged you sales tax ..I'd only be a couple dollars high. $4,897 delivered for a 22kW and a 200A SE rated ATS. That price is like a sore peter. Cant beat it.
Dont waste a mili-second on brain power on automatic vs manual transfer.
No reason. A 200A residential ATS is ~$500. Manual may save $50. You can make your automatic act manual you cant make your manual act auto.
A new 20kW diesel trailer unit is 3-4x the cost you will see above.
Not sure I follow about the shelter. You want to place the gen out there? Or you want to run additional power out there.
As far as removing and recouping....I just dont think it works. Charge a few $k more for the house when you sell. Use that as a negotiations, ok we will drop the price the k you asked but we are taking out generator system with us..bet they balk.