Ok, I guess I have three suggestions for you. I am a Eagle scout as well, and these are all knives I would have loved to have gotten as a gift, especially at that time.
1) Buck Custom 110, as mentioned above. This would be a cool present, and you could sit down with him to decide what blade, scales, and all he would want. Engraving, fingergrooves, there are a lot of options. A bit cool being able to pick it out just like he wants, but waiting for it would be tough.
http://www.buckknives.com/custom_knife_shoppe.php
2) Benchmade mini-Rukus. Nice medium to large sized knife, a bit smaller handle than a 110, and I would have just thought this was a very cool knife when I was that age. With the axis lock and S30V blade it should hold up very well.
http://newgraham.com/detail.aspx?ID=6619
3) Dick Atkinson small folder. With a 2.5" blade and titanium handles I think these are the perfect EDC. Its like having a mini-sebenza. I honestly think this would be the best knife of these three for this occasion, mainly because I know it would have been very useful to me at that time, and still would be today. And its a custom knife and still fits in your price range.
http://www.bladeart.com/artists/dick_atkinson/dick_atkinson.htm
Tell him congrats from us, and let us know what you decide. This really is a great achievement for him and i'm glad to see that you not only recognize that, but are willing and able to get him something that can help to demonstate how proud you are of his achievement.
schiesz