A hard money lender will usually charge between 8% and 10%. But you will save on the closing costs and any mortgage costs. Don't try going with a mostgage, since they will charge just as much in interests, sometimes even more + you will have all the closing costs, and other charges.
You might ask the owner if he/she would be interested in holding a 1st mortgage for a few years while you repair your credit - you'll save on closing costs and time - with 50% down it is very inviting. The upside for the owner is that the property may be worth more in a few years and you can make an offer at that time @ fair market value. Win- Win