6 builders can build a single floor 6 builders / 3 builders = <<6/3=2>>2 times as fast as 3 builders.
Thus 6 builders would build a single floor in 30 days / 2 = 15 days
There are 5 hours x 6 floors/house = <<5*6=30>>30 floors in total in 5 houses with 6 floors each.
Therefore 6 builders would complete the project in 15 days/floor x 30 floors = 450 days.
It would cost 450 days x $100/day/builder * 6 builders = $<<450*100*6=270000>>270000 to complete the project
#### 270000