At a garage sale this morning I found exactly what I've been looking for - a cheap CRT with composite video inputs to test the light gun I bought a while back. It cost me $2, it works (though it whines like bastard), and doesn't take up much space. It's an NEC N-3480, I think about 13", with two sets of mono composite inputs and not much else in the way of features. I plugged it in when we got it home, and Duncan was quite puzzled... it suddenly dawned on me that he wouldn't be old enough to remember a time before TVs were flat things that hugged the wall. No kid, some folks had TVs the size of pianos!
We turned it on and he immediately covered his ears... "that's the sound of scanlines, my boy". I don't have fond memories of CRTs whatsoever, and I don't understand the whole CRT-purist thing with retro gamers. This is purely for testing, so it's fine. Anyway, the lightgun works, and Duncan got about two minutes into Point Blank before learning he could put the gun next to the screen and cheat. Some things defy generations I suppose.
He's taken to playing PB and Time Crisis with headphones on, because the whine annoys him.
Anyway, at that same garage sale they had a pile of stuff in the back of a ute that was marked "free", one of which was an old computer tower. I picked it up, because it's a mid-tower, full-ATX case that I figured would work well for Duncan's machine (currently stuffed into an OEM HP case that's a pain to work with). Only problem was it's filthy, and I spent the better half of the day cleaning everything out, then Duncan and I transplanted all his stuff in.
I'm starting to look like a CoolerMaster fanboy - my case is a CM690, and this one is a Centurion C5... both absolutely ancient cases, but pretty spacious and nice to work in (absolutely zero cable management in Duncan's though). The case is a bit smashed up, so we'll likely replace it when we upgrade, but in the mean time it means it's a lot nicer if we have to work on his PC at all.