You can turn any truck into a submersible with very little effort. There are quite a few videos on YouTube to this effect. The really tricky part is getting the buggers to come back up again afterwards!
Easy - Put Donald Trump in it and tell the Persians (Or anyone really)
the maoster:
As for cost; cheaper than you’d first think, the example below was probably less than £9 per hour
First prize for best answer to a ridiculous question.
Carryfast:
http://www.youtube.com/watch?v=PLGIfVu_PQs 0.59-1.04 About as close as it gets.
There are plenty of examples of tanks having been made submersible in which case the question isn’t how they did it but how they found anyone brave enough to man them underwater.
While the better question would be how to put driven wheels/tracks on a submarine.
To be more precise they made American Sherman tanks float, not submersible,converted Shermans were called DD or Duplex Drive, first tried in WW1 using British Mk 1X tanks, then a Tetrarch tank was adapted. A Duplex Drive Valentine tank began trials on 21 May 1942.
Twoninety88:
Carryfast:
There are plenty of examples of tanks having been made submersible in which case the question isn’t how they did it but how they found anyone brave enough to man them underwater.To be more precise they made American Sherman tanks float, not submersible,converted Shermans were called DD or Duplex Drive, first tried in WW1 using British Mk 1X tanks, then a Tetrarch tank was adapted. A Duplex Drive Valentine tank began trials on 21 May 1942.
No the DD was an even worse death trap.
historyofwar.org/articles/we … anzer.html
youtube.com/watch?v=BthISvtWQMs 2.55-3.40
Safe and dry what could possibly go wrong. 
With the quality of modern trucks electrics you would have to be mad to consider it!
Theres vids of underwater bulldozers on youtube still running their diesel engines.