1. Your engine wasn't damaged by the sugar. Your fuel filters were clogged. ANY substance in your fuel tank that doesn't disolve is likely to block the fuel filters. Sugar isn't soluble in water. Period. Think about it.
2. What do you think that sugar would do, if it DID disolve in gasoline? Turn into syrup?. Well, If the sugar were soluble in gasoline, and you had 5 or 10 gallons of gas in the car, how much sugar would it take before you had any notable ratio of sugar to gasoline?
Ever tried to make a sugar and water syrup? How much sugar do you think it would take to make 10 gallons of syrup. Answer -WAY more than a 5 pound bag of sugar. Did somebody put 20 pounds of sugar in your tank? I doubt it.
3. If you want to test the "sugar isn't soluble in water" theory, it's as easy as getting a mayonaise jar, a pint of gasoline, and some sugar. From Wikipedia, here's a scientific explanation of why sugar won't disolve in gasoline... it's not magic or folklore -it's chemistry.
4. You didn't need your injectors replaced - or the rails- or the fuel pump. Your fuel filters (which are easily replaceable) are there to catch things that are insoluble -like sugar. They did their job and that's why they're clogged. Clogged filters means your car won't run since it can't get any gasoline to the pump or the injectors.
5. Why on earth wouldn't you change the spark plugs at 100, 000 miles anyhow? II understand that you are tight on money, but if you really replaced all the fuel injectors, you should have replaced the plugs at the same time. That could have been done with no additional labor and only the cost of the plugs would have been involved.
6. Having said that, the sugar will have had zero effect on the sparkplugs, and if you don't have the money, you can wait. You've waited 100,000 mile already. It won't run any worse than it would have before the incident.
Remember that the sugar couldn't get past the fuel filters to even get to the sparkplugs. Again. The reason that your car wouldn't run is that the fuel filters were clogged.
By the way, you need a new mechanic. A good mechanic would have done the cheapest things first (changing the filters) and then tested to see if the injectors need to be replaced. He should have also noticed that he wasn't getting any fuel to the injectors and replaced the filters before replacing the fuel pump. Either he doesn't know, or he's ripping you off. Either way, I'd say adios to him.