YOU are looking to spend a Pile of money .
Doing simple math , 28x40 =1120 sf .
In order to remove 1120 sf of earthen spoil from underneath an existing structure is going to require an enormous amount of temporary cribbing , using railroad size cross ties for cribbing or 6x8x4 timbers which cost about 20.00 each @4 foot lenght . To stack these 9 foot in height creating a Pier to rest your home on while removing the spoil ,and you'll need about 4 cribs every 8 feet ,rough math = 18 timbers x 4 = 72-timbers for each pier x 4 = 288 timbers, 288 x 6 peir sets= 1728 x 20.= $34,560 in timbers alone .These will be reset every 24 feet or so ,and then moved up successively as you Frame and pour foundation walls ,which will probably cost $60.00sf , pour 24x9 x 8"foundation each pour= 162 cf x $ 60.00 sf = $9720.00 or you could pour footers and set block walls under the home frame exterior, which would require you to pour footers on each side simultaneously and then set cement blocks to create a foundation wall on each side as you continue to excavate and reset your timber cribbing and so on and so on..................................The point being ,you are opening a can of worms attempting to remove the earth from beneath your structure and run the risk of the piers collapsing while attempting such a daunting Task.Of course we are NOT counting Architectual or Permit cost nor real labor costs !
Were we to run out the numbers completely , I would dare say and venture a quess between labor , material and equipment costs you would easily invest $ 150.000 to $185,000 in RAW costs ,much of which would be in material you could only resell to a Home Mover .
Your best investment , would be to relocate to a new home with a full basement
and give up the idea of digging out from under your home .
It is a grand Idea ,and as there are numerous contractors seeking work , I am sure you could find many wanting to accomplish the task,,,,,,,,,,,,BUT , The risks Out weigh the benefits ,unless of course ,You got a pocket full of money burning a hole through your pockets and creating enormous discomfort for You !
All of that being said ,It's YOUR Dream ,and if you desire , Follow IT !