I have a spotting scope that I purchased about four years ago for around $300. Image quality is VERY good (as I stated above) from 20x up to about 40x. Going beyond 40x image quality begins to suffer, losing brightness and contrast.

I personally believe that it is a myth that optics which produce excellent images have to be incredibly expensive. High quality (super transparent and homogeneous) glass and high quality light-transmission coatings have been well known for at least 30 years. And the cost of both as well as the cost of coating processes have been steadily declining ever since.

Speaking to that point, $300 rifle scopes from the best manufacturers these days are bordering on excellent. For example I have a $250 Nikon variable magnification rifle scope that I purchased about 6 years ago and optical performance is fantastic. Images are sharp and bright with incredible contrast at all magnifications. I am hard pressed to see how a manufacturer could produce anything with significantly better image quality at any price.

For reference there are two simple and important ways to test the basic optical image quality of your rifle scope, spotting scope, or binoculars. The first test is looking in low light to see if you can discern objects. The not-so-obvious test is looking under a bush which produces heavy shade with a bright-ish source just off to the side of it and behind it. If you can still see everything clearly in the dark shadow under the bush, you have an excellent optical device. If the bright light source which is just barely off to the side washes out all the detail in that dark shadow, your optic isn’t so great.

(Of course your optic has to produce sharp and focused images in the entire field of view at all magnifications–I figure that is so obvious that I did not have to mention it as an important test.)