With optics, form follows function to a great extent.
Yesterday, I was sighting in a new combination of rifle/red dot, and was adequately equipped with a cheap POS range rental that probably cost +/- $100, but was capable of resolving .223 bullet holes at 100 yards. Wouldn't want to rely on that cheap optic for much else, but it was up to the task at hand.
A week ago, hunting mule deer in big, open, desert country, I used a 77mm APO 20x-60x Leica spotter to note a tag (about half the size of a playing card) on the backside of the ear of a mule deer doe, in deep shade, at a laser-ranged distance of about 600 yards. The tag was easy to see (no, I couldn't read the number...). Even easier to spot was the white radio-telemetry color the doe was wearing... At today's prices, this is probably well over $3K worth of scope and eyepiece, not to mention the substantial tripod necessary to support it, it's necessary expensive case, and etc.
For range work, inexpensive scopes are fine. For serious trophy evaluation, etc., there's no limit to cost and quality...
For a basic discussion of optics, see my article, " How to Choose Binoculars" under my nom de plume, "jkendrick", at ehow.com.