Nate and Nuduray,
I am no expert on oscilloscopes but I spent a lot of time recently searching ebay until I found something I was comfortable with. I will give you my general impressions; maybe it will be a starting point for your own research.
I bought a Tek 2235A. I paid $287 + (reasonable) shipping for it, which was near an ebay record for this model. My seller claimed he was the original owner and had used it very little. It came with all manuals, 2 probes, and even the original plastic pouches for the probes. I saw nothing to indicate the seller was telling tales. The unit is absolutely pristine, including the probe pouch on top, which usually takes a beating very quickly.
I paid "top dollar" for mine because I got a $3000 (new) scope for 10 cents on the dollar and I didn't care as much what I paid ($200 or $300); I cared that it would work for me for many years without a problem. The cost of any repair that I can't do myself (or even a calibration) would be more than I paid for it. Same for many of the parts even if I could repair it. I wanted the dice loaded a little in my favor when I rolled it. Even in retrospect I am happy with it and I would buy another one if I needed it.
I have seen that model (and similar) go for as low as $100ish. It is amazing that the typical scope put up on ebay is described like this:
"I don't know what it is or what it does or even if it works. No probes, power plug or manual. No Returns"
More typically with a return privilege , maybe $200+, which is really cheap considering what they sold for new and the build quality.
Ebay is absolutely glutted with these things. You have to try to find something that actually works. If it doesn't, just the freight back and forth can be a significant fraction of the cost. The smaller scopes were designed as field scopes and a lot of them look like they have been kicked around a bit.
Most of these scopes are sold by liquidators. It might be a good idea to try to find one being sold by the user, just so you can ask questions and get intelligent answers.
For a while I put in a search for scopes within 30 miles of me. My plan was to try to go and look one over before I bought it, and at least plug it in and see it working, plus save the freight turnaround if I had a problem. I ended up shipping mine in because it was hard finding really nice ones locally.
Very few ebay scopes come with probes, which cost about $20 ea. and up. Factor that in to your price. A manual, at least on CD, will be very important because they are complicated beasts. You can buy manuals on Ebay, for widely varying prices. My manual includes several hundred pages of repair data, schematics, board layouts, part lists, etc. I might even be able to fix it if it breaks.
The 22xx series is a very basic scope, 100MHZ, no DMM, no cursors, nothing fancy. The 23xx series is a little nicer, some offering built in DMM (Which I didn't think was that important). Then there are later or more advanced and higher BW models that sell in the $600+ range with cursor measurements and other neat things; 4 channel scopes, etc. The 243x models are 150MHZ and digital. They are very common and sell for about $450 and up up up.
Some models come with built in diagnostics, which is very nice because when you get it, you need to accept or reject it quickly and you may not understand it well enough to know if it is fully functional at that point. Mine did not; it is a very basic model.
Scopes under the 100MHZ level sell very very cheap, even Tek scopes. As far as features, scopes have a lot of functionality designed more for TV and/or digital diagnostics that we don't care about. What we want is a nice wide bandwidth (100MHZ) so that if our amp is oscillating we can see it, even if it is a 40MHZ oscillation, and to accurately display square waves. All these 22xx 23xx model scopes are triggered, which is probably the most important feature. If you don't buy features you don't really need, you can get a very basic but very high quality Tek scope cheap. The sexier scopes seem to get more bids and more demand.
As soon as you get your scope you will want a function generator so you have a signal to run through your amp. I ebay'd a 4MHZ Wavetek 182A for about $100. That is a fairly common model. It is a decent basic generator and the square waves look ok up to about 100KHZ or so, which is all we probably care about. The rise is not perfect (a touch of overshoot) but it is good enough for what I need. If anyone is interested I could probably shoot some images and post it. A 4MHZ is probably a good bandwidth for these things. Lesser bandwidths will have more limited decent square wave range and higher bandwidth models get a bit more expensive.
Then I ebay'd a lot of twelve 6 foot BNC-BNC cables for $20 or so. I cut them up and make cables as needed. BNC connectors are expensive; I thought that was a decent deal and I have a lifetime supply of pre-crimped connectors. You'll want one BNC-BNC to connect to your scope's trigger; that simplifies the triggering and eliminates constant playing with the trigger level to keep the image stabilized. Another set or sets to connect to your various amp input jacks (3.5mm and/or RCA) and maybe a fallback set with alligator clips or grabber clips.
