Not trying to be snarky or anything, but if you are asking cost and mods needed to hit that power range, you may be getting in a bit over your head. While the stock bottom end is good for 600+, and with mods is capable of way more than that, you are talking alot of work (and some serious $$$) to get into that power range.... headwork, compression mods, custom injection setup and ecm, etc all are going to be needed to do that kind of power. I'm not trying to talk you out of doing your own build or not build it up some, but suggesting being a bit more realistic in your goals.
For starters, there is an excellent 460 section at FTE here---> Big Block V8 - 385 Series (6.1/370, 7.0/429, 7.5/460) - Ford Truck Enthusiasts Forums
I would suggest starting by doing some research there and seeing what works, and what needs to be done to redo a 460. This is the build I did to push into the 650+hp range with a 429 in my 90 F250 a few years back....

• D0VE-A block, magnafluxed, bored, decked, linebored
• Trick-Flow heads, ports cleaned and polished, ports matched to intake, Ferrea racing valves, Comp cams springs, Scorpion roller rockers
• Comp-cams camshaft, lifters, roller timing chain set
• 429 Crank, magnafluxed, trued, turned 10/10, lightened, oil holes chamfered
• Eagle H beam rods, floating wrist pin
• KB Hypereutectic pistons, 11.8:1 CR
• Weiand stealth intake
• ARP rod bolts, main studs, head studs, rocker studs
• Fluidampr harmonic balancer
• EFI converted to carb w/870cfm Holley
• Phenolic spacer plate under the carb
• Headers with true 3" duals, mandrel bent exhaust tubing
• Mallory 6AL ignition and distributor
• K&N Airfilter w/x-stream top plate
• Electric fan conversion
• Clevite bearings
• MSD timing control
• C6 trans, full TCI internals and stall convertor

This should give you an idea of the time, cost, and work it takes to start getting into 650-700hp range without the use of turbos, superchargers or nitrous. It took alot of work and research (matching the cam to the pistons and CR to run on pump gas) to do that build, BUT when it was done, it ran on pump gas (premium) all day long, and in a 1990 F250 4x4 ext cab long bed, w/3.55 gears and 315 tires, at 30-40mph it would downshift and break the tires loose if you stomped on it in drive, and a full throttle automatic shift from 1st to 2nd at 65-70mph felt like it was going to rip the rear diff out of the truck and leave a 20ft black mark on the road. The one time I did get into a top end race on the interstate was with a Lightning, and he could not believe a rusted, lifted F250 4x4 was walking away from him on the top end.

Anytime you start breaking the 1hp to 1cube ratio it starts taking work. Even more so when you are talking a big block, and when you have a big block and are going for over 1.5hp to 1cube, well, as it says in my signature...