Fuel Injection - explain this to me like I am 6 years old

I am now getting 12.5 mpg on my 71 Duster 318 4bbl. It literally runs fantastic, finally.

I have been thinking about installing electronic fuel injection. Price is an issue for my wife at this point in time. Would like to keep it at $1,000 or less.

Does this sound do-able and would it be worth it? Would it dramatically help my mpg? What advantages is Fuel Injection.

I know very little about it and have not really started to educate myself on it. I know that on my other cars there are injectors for each cylinder, and the after-market seem to use one injector in place of the carb.

If it makes sense to do, I will at that point learn what I need to know.