how old's your son, does he need a youth model?
i've only shot trap with my clays/hunting/blasting/all-purpose mossberg 835. pretty much competes with the remington 870. just a good, versatile pump gun, coming in around $300 give or take. i'll probably get a remington 11-87 some day, but i think unless you're getting very competetive it's unlikely you'd need a dedicated gun for clays. maybe i'm just nuts. function defeats form in my book
... well most of the time. when i can combine the two that's great. and it doesn't apply for women.