If you do not want to be upside down on the car when completed, walk away. However, the caveats are, 1- you have a lot of the parts already, 2- you do a lot of the work yourself; that will save you a great deal of money. But would it be enough to keep you upright? Probably not.
Another way to look at it is this, if you intend to keep the car for a long time, your investment may catch up with inflation in time. If you're looking to flip it soon after completion, don't waste your time, parts or money.