Kim, I'm not trying to be sassy, but it would probably be cheaper for you to move into a house that has more room. The wall building, excavation to allow new footers and walls, waterproofing of the new walls, and then excavation of the dirt--before bringing in gravel for and the pouring of a concrete floor will be a major undertaking. Then you will probably have to fix the plumbing and drywall or plaster that you broke upstairs. The work that you say will be done by you is the easy and cheap part.
Jacking and blocking the house to install the basement walls will be an expensive, dirty, messy job and one that is for someone with a lot of experience in that area. And you have to think about things like egress windows if you want to make that basement room liveable. Do you know how to get a building permit? You will need one for that project. Really, moving is much easier and cheaper! I'm sorry that's not what you want to hear, but it is the truth. And local building expenses and requirements vary all over the place.