Well, Stephen, that's the thing. Maybe 10m, 12m and 15m will not be doable. Or maybe they will, mostly. This is the advantage of an analog scope. That 20MHz spec is where the scope can guarantee a particular magnitude, but at 30MHz most scopes will still produce a waveform, just one that's no longer valid in magnitude.
This might be just fine depending on the alignment procedure. Sometimes you can use frequency counters or beat matching to augment. There is actually very little in your radio, all radios, that is at RF. Things are mixed down to IF quickly because it's easier and cheaper to work in KHz. It's likely that with a 20MHz scope you can do 90% of what you need, even on VHF radios. And you can adapt, set your trigger to 1/2 of the frequency. I mean, a 15MHz trigger might just be every other rising edge of a 30MHz signal, right? You're not building spaceships here, the accuracy is more than sufficient for a boat anchor.
For a digital scope, the sampling rate becomes your limitation. So for a 29MHz signal you need at least about 150MS/s to achieve any sort of accuracy.
My $0.02 is that a used analog scope should fall in the ~$150 range and I would try to talk both of these 20MHz guys down. But I'd probably watch for a 50~100MHz scope, then there's no question. Test equipment is like radios, you can always find a use for it. :-)
"Silent enim leges inter arma." -- Cicero