My older son was in a private school for four years. The first year or so, I only bought his uniform pants (navy) at places like Target, Old Navy, Kohl's, or JC Penney. Every pair of those pants ended up with shredded knees and I was having to buy new pants 3 or 4 times a year! SO...I broke down and purchased the pants from the local school uniform store (most of them have triple reinforced knees). From that point on, I never had to replace his pants during the school year! My point is that the initial outlay may be larger, but over time, it may be less if he is that hard on pants!
I know this wasn't exactly what you were looking for, but I have been there, done that and this was my solution!