i think that the food dyes last longer than kool aid and yes you do have to add acid ..thats what helps the dye stay on the wool.
the only downside to using those dyes is that they can fade in sunlight and over time.. if you are wanting the color to last i would invest in a higher quality dye like jacquard acid dyes (or other brands).
using the food dyes though is a good starting point if you aren't sure you are going to like it or want to experiment alot.
the process of making yarn from fleece to finished yarn can be cost effective or more expensive..you have to factor in the cost of the fleece, the water/soap you use to clean it, the dyes and possibly your spinning equipment
i've found that the cost takes a backseat to being able to make things with your own handspun (or hand dyed) yarn..it's wonderful ..def not nuts!