Full front fender. That's where most of the spray comes from.
Wool socks are nice if they fit in your shoe because they are warm even if wet.
SealSkin socks might be worth looking into but it's been awhile since I wore those.
Part of the problem is that even if you waterproof your feet the rain will run down your leg and into your sock. So beyond the fender think managment not sealing off.
Newspaper in your shoes at work will help absorb some moisture. Putting them on the back of a computer monitor (if you have a CRT)will definitely get them dry.
For cheap solutions neoprene shoe covers or the Endura shoe covers work quite well.
Thought about just leaving a pair of shoes at school or wearing sandals?