I'm looking for something from the 80/90's, affordable, simple, from a good brand, nothing fancy but perfectly capable, that sold a lot of units at it's time so there will be more chances of buying one second hand and with widespread information and documentation in case it needs repair in the future.
I know I am not an expert since I just recently bought my own for the first time. I got many good advises about buying a used one to learn with and I suppose that could be a great idea… If I knew it would work properly.So I I went for a new one..
Not really a recommendation, the B+K 1479B 30 Mhz has served me well over the last 15+ years, and meets your spec's. Not many bells and whistles, but all the basics are there, including the very useful (to me) differential input function between two probes. Adds ch A + B, and invert ch B polarity for A - B.
One thing I really didn't like was that the Service Documents were quite bad, confusing and lacking info.
It's quite the opposite from any Tektronix or HP Service Documents that are really tight and complete.