Just some thoughts...
Red lines, as above, definitely. The "red lines" are on the wheels. Also there are some that came in different colors (think card variations) where the common color(s) are dirt cheap but the rare ones can go for big bucks. If you haven't already done so, make sure they are all hot wheels and not some other brand mixed in. If so, separate them (though some 'off' brands are worth money too).
To sell them, I would put them in lots of 5 or 6 cards (as mentioned), maybe similar style vehicles and put them on ebay as an auction with some good pics. Especially if you don't want to spend too much time digging up information. The auction style should get you close on a reasonable value for them.
Donate what doesn't sell to your grandson's store where he can put the used ones in the 2 for a $1 bin.
