How do price and quality relate in blenders?
Like any other product, price and quality don't always relate.  However, here are some notes and features to help you:

What food stuffs you can blend in your blender and expect good results, how often, and for how many years depends on the following:


Quality of the motor:  When the material you're blending gets hard to blend (say oil separated peanut butter mixed with dry almonds), you can easily send the blender up in smoke.  A better blender might hit its maximum-current/temperature switch, shut-down, and protect itself.  An even better blender might happily blend (saw a giant one with the motor made by Harley Davidson, it didn't care what it was mixing).  See the notes on power/wattage.
Speed of the blade (RPM):  Cheaper blenders tend to only reach a couple of thousand rpm.  The Brand you're (not)mentioning can go near 30,000rpm.  At that spin-rate, frozen fruit starts looking like Gelato (smooth and shiny).  In a $20 blender, they look like frozen fruit slushy with ice crystals remaining relatively large.
Wattage of Blender: Generally the higher wattage blenders are more powerful, although not in every case.  This is again one of those features that leads to being able to make apple/carrot/beat juice in your blender or make a contribution to your local appliance landfill.  Top Gear tried to make a Beef, Bovril and Brick smoothie with a V8 Engine.
Intended use: Commercial blenders are designed to be running practically all the time (like the ones at StarBucks), hence the $2000.  The 'Prosumer' ones, might heat up if under heavy and long duration use and shut-down for a few minutes at a time.  The low-ends can last you a lifetime if what you're blending is not very thick/viscus and you don't keep it running for long sessions.
Quality of the Jar, Blade, and Gears:  In the low-end of blenders, the ones with glass jar might be better since they're easier to clean and don't get foggy.  The high-end blender manufacturers (sort of) treat the jar as a consumable that you'll have to buy once in a couple of years.  Fresh blade, and clear jar.


Pro-Tip: Sometimes it costs you an extra $250 to get the model with the adjustable speed dial.  While there normally is a perfect blending speed for any given 'input', you're looking at diminishing returns since the two-speed type will blend just as well given minimally more effort.