THIS!! A good running store will observe your son's gait and show you a range of shoes that match the way he runs. It will likely be cheaper to buy at least the first pair of shoes this way than go to DSW or someplace like that and get something that just feels good and may well give him a problem down the road. Pain and doctor's co-pays are the likely results of a pair that isn't a good fit, given how many miles XC runners put in. Once you have a pair that work well,you can always go on-line and find better deals for the next pair.... and he may go through several pair in a season, depending on his mileage.
Tip to drying wet running shoes (and you will have those OFTEN

) Pull out the insole, loosen the laces and stuff the shoes with crumpled newspaper. If the shoes are absolutely soaked, you may need to replace the paper once, but by the next morning the shoes should be dry. We don't recycle newspapers very often during XC season and keep a big stack of them around for just this purpose.
Good luck to your son, hope he enjoys running!