Ive gotta agree with Mr. Yount on this one. If you convert it "right", the costs can add up quicker than it seems when you factor in that to do it right, you've gotta redo the gas tank with the proper sump, get the right fuel pumps and regulators, distributor and all the supporting ignition.
That said, it CAN be done VERY cheaply if you pick and hunt for parts through a junkyard. If you do your homework or maybe find a donor stock carbed Mustang, it'll make life easier, but only if you're going for a very basic setup.
IMO, i like carbed cars a lot. I like the overall simplicity of a carbed engine's appearance, and the fact that it doesnt take a bunch of computers to tune a carbed motor to perfection (that's not counting a good dyno tune). I like the fact that you can build a pretty stout motor with carbed parts for pretty damn cheap vs. an EFI setup. I especially like the lack of wiring harnesses and sensors and all the other BS that comes along with EFI motors.
Aside from all that, i think that if money is no object, or at least to say that you've got a bit more money to throw around, EFI is the superior of the 2, and that's coming from a guy who's building a carbed car. It's just proven that you can build reliability, economy and insane power with EFI, it's just gonna beat up your wallet to get there. Also a major advantage with EFI would be daily drivability. I myself have no problem driving around a car that takes the occasional high reving to settle down the idle, or a wild cam or a huge stall, but with EFI you can have a crazy cam and make gobs of power, and the EFI pretty much does the hard stuff for you.
I recently went to a cruise-in with my local Mustang car club, and we had a 7 second Mustang in attendance. I'm not sure how far, but the guy drove it there and back with no problems, and i'd say he drove a reasonable 40 miles round trip to make it. It was a supercharged EFI motor, huge intercooler, enormous stall, powerglide transmission....all the toys that get a Mustang into the 7s. I found it VERY impressive that the car was as streetable as it was. He left the place and pulled right out into traffic like he was in a Geo Metro and went right along with the flow, although scaring the ass off of every sensable driver around him (open headers and power somewhere around 2K HP tend to scare soccor moms).
Lastly and i think this has been mentioned, if you switch and have to pass emissions you can't make it work, even if you were to put a stock carbed motor in your car along with all the emissions equipment, and even if you still passed the test with flying colors, most states don't allow changes in the motors by year like that. I'm lucky enough to not have to worry about that.