No, you can't do 50% cut without a solid envidence back up. What you should do is: let your agent to do a sales comps to figure out what's the market value should be IF the house is in a know, good, standard condition, then bring a contractor to do a repair estimate. Your offer price shall be market value - repair cost, maybe cut a little more.
If you are the cash offer, cut another 10% ~15% to set your offer price. You can submit the offer along with your agent's sales comps and contractor repair estimate, thus you can convince the seller (bank).
Good luck!