Septic tank and well will be expensive. Just how expensive depends of where you are. Power also can be pricy depending on who serves the area. And this will immerse you into the permits and inspections swamp. That is one disadvantage to putting a mobile home in you will have to deal with the code enforcement people and down south in hurricane country installing a mobile home is not straight forward involving major steel tie downs embedded in 6 feet of concrete from what I've heard.
Not so with an RV but you still need water, power and sewer.