318,340 or 360?

ok sounds like 360 is the way to go what kind of price would i get into for a junkyard motor or would i do better to find a car with it already i dont want to spend to much and i want it to get decent milage like at least 10-15 but thats not so important i live in a small town how much would it cost to build to like 350 horsepower and a good bit of torque im not realy sure about what affects drivability and what not in a motor my dad did some offroadin when he was younger he had amc 360 in his jeep with an rv cam but he wasnt much into engine work so im tryin to do the research before we get the project so ill have more of a plan thanks for helpin