If you're just talking about a block foundation, you'd have to dig footings by hand all the way around. Then, you'd have to pour concrete and set anchors for tie down straps. Then, you could lay block up to the sides.
I had my mobile home (single wide 14x70) set on a pre-poured 4" slab with 24" wide by 12" deep footings under the I-beams. They then set the anchors and strapped it down before blocking up the foundation all around. The total job (slab, move, setup, and foundation) was $7500.
If you're talking about pouring footings under the block pillars without moving the mobile home, you'd have to dig 24" square by 12" deep holes between the existing pillars and pour concrete. Then, you'd have to get a mobile home moving company to come out and jack it up, build new pillars on top of the footings, and relevel it. You'd probably come out cheaper to pay a moving company to move the mobile home off the lot, then pour all the footings before moving the mobile home back to the lot.