My parents did this exact project to their lake house back in the late 80's. I'm pretty sure that they used James Piscopo out of Belmont as the GC. Anyway the house was on piers and they had the house jacked up. They used hydraulics to lift it and then an excavator dug out under the house before they poured a concrete foundation.
Just like your situation the house was lower than the street. After the house was jacked up it was level with the street. This created a walk out basement. All in all I believe they were very satisfied with the results.
Not sure if there were any "hidden costs." Just remember once you get into this project significant electrical, plumbing, heating, costs. My parents had an extra bathroom put in the basement. This required plumbing work prior to the concrete being poured. It is a good opportunity that you want to take advantage of. Even if you just have it roughed in and wait to finish it later. They put in a utility room with the heating and hot water tank in it and had that room plumbed for a washer drier.
After re-reading your post you said "usable." Did you mean as a living space? I just assumed you did. If so carefully consider the plumbing issues I mentioned. You'll kick yourself later on if you decide to do add a bathroom/laundry room and your jackhammering the concrete floor.
