Paint is the cheapest thing that you can do to make a house more appealing. Linoleum is cheap and durable, but you have to use it sparingly or it looks cheap. Cleaning the carpets will sometimes be an option to replacing them, but dying them might be an option (I’ve never done it but have heard of it being done). Stay away from replacing cabinets and fixtures if possible. Rework, paint and repair existing items if possible.