Lots of good suggestions in this thread. I would skip the hollow handle knife all together, most are sub standard, the good ones are well above your price point. My vote goes for the Ontario Pilots Survival knife. I had one at his age and had many adventures with that knife. I also learned how to start sharpening knives with the stone that came with it. Glad to hear your boy is doing well with Scouts & enjoys the outdoors.
i agree. as much as it has been put down in the past on this forum and for the most part on the internet, they are hard to beat for there price. they have a sheath that can put up with a pretty good beating before it even thinks of kicking out on you, it has the "classic survival/kabar/rambo look", it has a sharpening stone incorporated in its system and all sorts of ways to store small hooks, small ferro rod blanks and what not. every one has also been saying that saw backs arnt worth the time of day and for building a shelter such they arnt, but i must say for harder materials like concrete (and the skin of an aircraft i guess??) they work fine. if he feels he will enjoy having them on his knife then he should by golley! i still find my self playing with mine even though i now have knives of better quality. there just that fun.
http://www.youtube.com/watch?v=IEswq8prS-0&feature=channel
when i was reading the question this video came to mind
this one might help as well
http://www.youtube.com/watch?v=-cTo5MR2SdQ&feature=iv&annotation_id=annotation_682692