Someone with more experience can weigh in, but I can offer some general info. First, as has been mentioned, you don't need a top-of-the-line instrument. Frankly, I don't know how much quality you
do need, though. The differences between lower and higher quality are (and I'm sure I'm leaving something out):
-How well the overall scope is machined; whether course/fine adjustments operate smoothly or roughly over their entire range.
-Features: Does one type of scope have lighting, for instance that another lacks?
-Optical quality: This breaks down into the following areas:
Precision grind of the lenses
Precision fit/alignment of the lenses
Coatings of the lenses
Glass quality of the lenses
I really don't know what the overall fit/finish and the optical fit/finish is like on the cheaper modern scopes. As for the optical quality, coatings on the lenses degrade over time, and can give a "mottled" appearance to that which is viewed. In my personal experience, I've never found this to be a deal breaker. In fact, I'd personally prefer degraded coatings on an older scope that has lenses made of low-iron glass with superior fit to a modern scope with better coatings.
This is why I, personally, would buy a $200 used scope from the 80s rather than a newer inexpensive scope. It's a gamble though, in that you don't have a warranty, might not be able to return a defective scope, etc. I know that eventually all binoculars will fail as a result of moisture intrusion, though I don't know how long this will take. Some binoculars made in the 80s have failed, while some made in the 40s are still going strong. I might be comparing apples to oranges, as I don't know if this is a problem with microscopes.
I just really want to brings the above up for discussion. I'm not an expert, and will let others with more knowledge comment. All in all, I don't know if you'd be better off spending $200 on a new cheap scope or an older used scope.
