original 100-400 vs 70-200 w/ 2x extender III

want to shoot grand kids sports, hockey and baseball. I also attend several minor league and pro baseball games every month. All the pics are for personal use. On occasion would sell a few prints to other families.

Was looking at used 100-400 about 900 or extender for half that cost new.

I know you loose 2 stops but is the image quality that much different with the extender?. I am not a pixel peeper. I look at color, contrast and emotion in photos.

I think the question you need to ask is whether the AF speed can keep up with action when adding the TC to the 70-200. I know the 100-400 can because I shoot lots of action with mine. TC's slow down the AF but by how much I don't know relative to your needs.

Normally i advise strongly against the idea of using a 2X with a zoom to get to 400mm.
But if it's just for a rare occasion, and you also happen to have a zoom that handles T-Cons raterh well, your solution may be worth while.

that said, I like the old 100-400mm a lot and think if you got it you might find a lot of other uses for it.