Unless you drive it a lot it will take a lot of gas saving to cover the cost of a motor or trans swap. Use the money to buy a little car and use the van when you need a van.
This one is the winner.
Swapping motors or transmissions just to save money on fuel mileage is a vain effort. Even if you could increase your mileage by 4-5 more mpg (which is pretty questionable in my opinion, 1 or 2 mpg improvement is probably more realistic), at $5 a gallon gas, how many miles do you have to drive to break even with the cost of whatever you swapped in? Will you drive it enough miles to make it worth the effort?
