418 Stroker options....
I just put together a 408" stroked 360 Magnum. It has 10.2 to 1 compression and runs on pump gas. It is injected with a modified factory OBDII set-up, gets good mileage and can either be a kitten or a tiger depending on how hard you push the gas pedal. My mild build is likely turning out somewhere near or just south of 500 hp with the mildly ported and Super Prepped Hughes supplied Edelbrocks , Airgap Intake and Big Gulp throttle body on it.
It's extremely quick out of the hole and has a scary fast top-end charge with a 4 speed automatic running a 2.73 first and a .67 overdive, Precision of New Hampton 3000rpm stall converter and 3.91 rearend gears. With a little practice and warm tires, I can almost dead hook on the street with 275/60-15 Nitto Drag radials.
It cost me about half again what your upper budget is for just the motor, and probably the same for the rest of the drivetrain, fuel system etc to allow it to put the power to the ground and still be able to go cross country.