if your car already has the pushrod 5.0, that would be the cheapest way to go.
If your car already has the 4.6, that would be the cheapest way to go.
In either case, if you're swapping what you don't already have into your car, you have a lot more to be concerned with other than just how much power you can get.
How much power you get out of either one depends entirely on how carefully you select parts and how much money you're willing to spend, both before it's built and when you get to the "tuning" phase.
Before you plan the build, you have to establish the operating parameters of the car. It's probably going to be mostly a street car, so you have to establish the "driveability" parameters. A stout pushrod motor won't idle as politely as a stout 4.6 because the 4.6 will have the computer controlling cam timing.
You also have to ask yourself if you want to pay someone else to tune the car for you. With a carb'd setup, you can do it in your garage. With an EFI setup, you gotta take it to a shop.
To do a proper build on a 302, it's gonna run you at LEAST $4k. When you start adding the extra (but not a bad idea) items to the build, you can quickly approach/exceed $7k for a fully assembled engine, from air cleaner to oil pan.
Finally, you have to consider the rest of the power/drive train. Can it survive the additional power?
Engine builds/swaps ain't rocket surgery, but they still require serious and considered thought.
I'm currently saving money for mine (I need $25k), and won't even start the process until I have all the money I think I need to at least buy all the parts ($19k).
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427w, Tremec Magnum XL, 3.73 Too many mods to list - go here: paddedwall.org/2012mustang/Default.aspx (Intentionally pissing off badge Nazis everywhere) Engine swap by Two Ten Performance (twotenperformance.com) in San Antonio