You would need a transfer switch...so that you don't collide with the power companies power...
You can get a 16k generator with a transfer switch for $4k... Electrician if you don't do it yourself will be about $2k depending on situation...could be 1.5k... then you have a plumber if you don't want to do the LP hookup probably about $1k depending on how far a run it is...
https://www.homedepot.com/p/Generac-Guardian-16000-Watt-Air-Cooled-Home-Standby-Generator-with-Wi-Fi-and-Whole-House-Switch-7178/311540322
Spike