First off, let me thank everyone that replied. Even if things got off topic, I learn a lot on here often as a result of threads going off topic.
Thank you for all of the great advice. I'm going to sit down with my son and give him some ideas and let him mull them over. While he makes better money than I did at age 11 ($2 per week seemed like fair wage back then), he obviously does not make enough money to afford to buy all of his own gear. Nor would I expect him to. I'm excited that he has expressed a strong interest in investing his money into scuba gear, at a cost of not spending it on video games (I'm looking at you, Modern Warfare III!). I'll find some way to make it equitable for him, even if it means I buy the regs and he buys the hoses!
Having had 2 regulator failures in the past month, I'm a bit leery of encouraging him to buy a used regulator when neither of us are trained or skilled at servicing it. Like others here, I have bought a lot of used scuba gear for my own use (and some for my wife's use) and don't generally have an issue with it, but the difference between buying used fins or a used wetsuit and a used regulator is that I am qualified to inspect fins or a wetsuit, I'm totally new to the DIY regulator servicing and have never spent enough time taking one apart to understand how they work. That is my failing, not his, and I may buy some vintage gear so that we can both learn more about it. His goal in life is to work for SpaceX, and he's inquisitive by nature.
As for the long hose.... he's a kid and I dive a long hose. Is long hose better? That's another thread. Should you use a long hose when rec diving? That's another thread. Either way, I know it would make him feel good diving the same type gear that I dive, configured in the same way. It might not be perfect, but what really is? I am hoping that in the next few years he and I can take GUE fundies together, as I know my wife isn't really interested in it. She's been my dive buddy for 200+ dives, but she has zero interest in DIR or GUE or tec or overhead environments or anything outside of relaxing open water fun dives. She did manage to put up with me and get every non-professional PADI cert available before our son was born.
I have an opportunity to get a very sizable discount on regulators made by the following brands (it's a one time offer personal from a shop). If you have any recommendations within these brands, I can buy them new at a discount that puts them a bit under what I see used pricing going for here or on eBay. Brand list: Halcyon, Dive Rite, Atomic, Scubapro, Hollis, Oceanic, OMS, Zeagle, Apeks, and Aqualung.
Lastly, to those that suggested vintage gear - one of my bucket list items is to dive a vintage double hose rig.
