Wow - I don't know. I'm in the same position as you - I'm trying to get some for my kids to trade for our summer trip, but they just want to have fun trading while they're there, then they go into a box in the basement not to resurface ever again unless we go to Disney again (and I'm pretty sure this will be our last trip). Mine like trading for the CM or LE pins, only because the CM's tell them that they're "cool" but otherwise seem to just trade for what they like.
I was all set to buy from mousepinsonline until I read noodleknitter's comments. I did pull up the seller she recommended, Harval1, and he had sets of 50 for $100 which isn't too much more than the seller you're looking at (per pin), but that was the smallest number you could buy. I guess I'd just be concerned about the "they don't look like the ones they sell at WDW" part. I'm concerned because my kids aren't the cute 2-4 year olds that any CM will take anything from because they don't want to upset them. 2 will be teens when we go (and the other 12), so I'm sure that if they have "untradable" ones, CM's won't be shy to tell them no and I don't want to get in that position. But I also don't want to spent $7 a pin.
Think I'll go with Harval1 and get 50 and hope most of them are tradable! Let me know if/what you do - good luck!