Backing out of a contract, past the inspection period?

[Sinh T Tsang]

I have signed an agreement with a seller that seems to really want to get rid of his home quickly. The home is for sale in "as in" and "cash sale" with "ZERO earnest money deposit" under a standard "Louisiana Purchase and Sales Agreement".  It has been past my 15 days due diligence, and it is on the 19th day. I have told the seller on day 19th, that I want to back out of the contract. The seller insist that he will sue me and get with an attorney and will proceed with his actions on his end. He insisted that i move on and proceed with closing on his home or he will take actions.

QUESTION: What are my requirements to close on this home? And what are the options that I have to get out of this?

I have walk with several experience investors but they told me that it is too expensive to fix. Could be in the range of 30-40K, much more than i anticipated because it requires structural renovations as well. The area home sold for that is only around 45-55K comparables, and it was under contract for 18K. At first walking the home, i believe it to be only cosmetic, paint, flooring, cabinets. But it looks like there will be structural roof suppport, drainage, and insulation, and rotting.  So I told the seller I want to back out on day 19th. But He insisted that i told him too late and by the contract, I was suppose to inform him before the 15th day. 

What options do I have? Should I be overly concern? I sure as heck don't have the money to do a 40K renovations, plus going over the price of what is it actually worth. I thought the renovation would only be in the 20K Max. 

Thanks