ALOT!!lol. What year is your car and what fuel pump and stuff are you using right now. If its all carbureted mechanical stuff then you have quite an uphill battle going for ya.
$400-500 intake
$100-300 injectors
$100-200 throttle body
$200-400 wiring harness
$200-300 MAF crap
then you still need an EFI 351 distributor, and then an electric fuel pump to support the EFI fuel pressures, and then any misc. junkyard stuff like the steel fuel lines, wires, blah blah blah. I dont think its possible for under $2000 since you need performance parts to support the engine and because its a 351 and not a 302 so parts are harder to find and more expensive. I'm pretty sure you can use a 302 wiring harness which you can buy everything from one of those mustang junker places where they strip mustangs and sell the stuff. Couple of those guys in all the magazines. Tell them you need everything to go from carb to EFI. I think they sell the entire computer/wiring harness in one kit. Then use a MSD 351 dizzy which should connect right into the wiring harness if you get the EFI dizzy. Again, use 302 fuel rails and stuff, and probably 30 lb injectors, and a 75mm throttle body. For the intake use a vic jr. Its designed for high rpm 302s so it will definitely flow your built 351. Hope this gives you a better idea.