For under $50,000 the only reasonable choice is to use a bank or credit union. As an investor the FHA 203K construction loan option is not available for repairs, like it would be for a owner occupant buyer.
If you put down about 25% and the house is habitable, you can probably qualify for a the purchase price if it appraises, but will be on your own for improvements.
I can introduce you to a couple of lenders that may be able to help. Call me at 623-239-6919