I would talk to a septic tank guy before considering buying. New lines will be $5k at a minimum and depending on the size of your lot might not even be possible to replace. Do you know if county sewer is an option? $1200 rent is a bargain for a decent house right now. I get that for a900 sq. ft house. Any 3 bd 2 bath will cost you north of $1400 easily. If you want to get a quick idea of the value fixed up, you can Zillow your address and click on the map and see what the neighborhood houses have sold for.