Old park homes sinking

Bought a small park in WI. Park is 50 years old and it appears there was virtually no site prep for the homes and they have settled quite a bit.
The city wants me to raise each home so the furnace vents are 25” off the ground. They want me to raise each home, add a 6” gravel base, set the home on piers and tie them down.

I have 13 lots and have been quoted 3,000-3,500 each for the work.

Does this sound like a reasonable plan? Any alternatives available?

Thanks for any input.

You could decommission the central heat and put in AC + Heat window units. Then the vents on the ground won’t matter. This will cost $1,200 to $2,000 for a 3/2 home depending on the approach you take. The electric bills would be higher in the winter if the furnaces are gas today, so it might not make sense in that scenario.

Confirm this is acceptable with the city before proceeding.

Keep us posted.