Good posts by JWarren!
I would add these comments:
1) Internal adjustment range:
The bare minimum adjustment range required of a long range scope will depend entirely upon *your rifle's* exterior ballistics. Rifles such as the .308 will typically require 38 to 44 MOA over the base 100 yard zero to be dialed on at 1k. Other cartridges offer better ballistics, less drop and thus need less internal elevation capacity. The 6.5-284 and .300WinMag often require only 25 to 28 MOA under the same conditions. The ballistics are not an exact number, since variations in *actual* muzzle velocity, crosswinds, ambient temperatures and density altitude will change drop figures at 1k by 1 to 2 MOA or more.
The internal adjustment must be actually measured to determine how far it goes. Many scopes, my Leupold 6.5-20x50 Vari-X-III for example, continue to click, but the reticle ceases movement. Further, some so not offer adjustments that correspond *exactly* to the value stated. Some "1/4 MOA" scope adjustments actually render 1/4" at 100 yard changes, so, there is a built-in 5% error To test the actual movement requires a graduated collimator or actual field testing.
2) Adjustments:
A large portion of the costs of high-end scopes are tied up in good quality accurate and repeatable adjustments. Scopes that do not offer positive reticle movement and must "settle in" are OK for hunting or range work, but have no place in long range precision work. I would rather have slightly lesser glass quality than to have poor adjustments.
3) Eye fatigue:
Glass (image) quality cannot be fully evaluated by simply glancing through the scope. People often say "I've personally done a side-by-side comparison and the image rendered by XYZ is no better than ABC". This statement may be useful to the hunter or casual user, but not necessarily to those who spend extended times behind the scope. The human eye is an amazing and wonderful machine, capable of adapting itself to a wide range of focus and color irregularities. Those shooters who spend extended periods of time behind their glass shooting matches and/or spotting for others will quickly notice the difference in eye fatigue at the end of the day.
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While the scopes listed above by several of the posters are excellent scope *for the price*, it will be up to the user to determine how much the various performance nuances will mean to their individual use.
If casual use over short periods of time of a target range are the norm, less scope is needed. The demands of high-contrast bulleye shooting on a range for a couple hours at a time and where shots can be walked in to the black are minimal.
If one anticipates long sessions shooting at targets that may be blended with background clutter and where first round hits are critical to satisfaction, it is much more important to invest in good optics.
While it is tempting to consider the couple hundred dollars savings on initial purchase price, this is not the big picture. Sure, there are a LOT of cheaper scopes out there that do "good" jobs, "for the money". Also know that over the life of the scope or shooter, even spending $500 more on a much better scope can amount to numbers like $20/year . . .
My suggestion would be to do some serious consideration of your needs and go from there.
This article is a very good evaluation of low cost scopes:
http://www.longrangehunting.com/articles/low-priced-long-range-scopes.php
If you ultimately decide a higher quality scope is required, used Leupolds are often available at reasonable cost. The "For Sale" sections of this forum, and the classifieds at LongRangeHunting.Com, Sniper'sHide.Com, BenchrestCentral and other forums often show good buys on VERY good scopes. M1 turrets are the most convenient to use, but the target turrets aren't bad either. Either Mil based or MOA based reticles are great tools for the long range shooter and almost indispensable for tactical matches and field shooting, but the scopes with duplex reticles are often around for far less and still quite useful. I'm sending you a PM with one example of a ($650) Leupold that would be an outstanding deal if it meets your application.
Good luck,
Ed
