Cost To Add A Basement
I don't think ANYONE can do that from here. Really, now, you I can't imagine how we could do that.
Take some pictures to a Contractor (of your garage and the surrounding 'area', and ask him. Make sure you write down EVERYTHING you think you might want to have done. I don't think he's gonna spend too much time on your 'request' if you're only looking for a number and NOT to have the job done. If you're serious about this, go IN PERSON, and ask what he needs to know as far as what YOU want in your basement. If you just want an UNfinished basement, that's easy for him to do. But if you want a FINISHED basement, you have some 'work' to do for him.
My best to ya and hope this helps.
Jay J -Moderator