Since I've noticed a lot of people just trying to go cheap, but then complain that they fit weird or don't have enough crotch space... I'm going to post this link.
Shitty cheap pants will fit shitty and cheap. Find your waist size, figure out what size leg opening you like (14 is super tight, 16.5 is usually straight slim, 18+ is relaxed) this is how wide the circumference of the leg is. Some pants will list is as 7.5,8,9,ect.. because when laid down it is folded in half. Also pay attention to RISE, this is how much room is from the tip of the crotch to the waistline and will affect your lil dudes comfort.
There is free shipping here, so just find a solid pair from the sale section, check the leg opening, and BOOM you got some quality pants that wont hurt your crotch.
http://www.tactics.com/casual-pants/sort-3