Yikes, Am I in over my head??...Any suggestions to save this deal

[Remona Castle]

I acquired an off market property a couple of months ago. Its a SF home, 3/2/2, 2700 sq ft on a large corner lot (3/4 acres). Loads of potential. Estimates from two different GCs showed rehab cost at more than twice what I budgeted for (170K). I am in a HML and the monthly payments are up there. I am getting nervous because I don't have enough cash to cover costs. Any advice on how to save this deal. Here are some stats: Purchase - 260k; ARV 500k; House needs a little of everything and a lot of some and to get max ARV, leverage current square footage add a bedroom and bath, making the home a 4/3/2; with two master bedrooms. Any suggestions on what to do to save this deal....