Hmmm.... I just went to www.everymac.com, and it's saying $200 for "Apple iMac Core 2 Duo 3.33GHz 21.5in Aluminum 1TB A1311 BTO 2009" in excellent condition (after being redirected to buybackworld.com). That sounds more in line to me than $700 to $900. I just recently bought a new iMac to replace my 21" iMac from the same time frame. Gazelle.com offered me $127.
When you do sell it be sure to prepare it for sale according to this Apple document: What to do before selling or giving away your Mac - Apple Support. Also be sure to include the disks that came with the computer originally. If you don't have them then you can get them from Apple for a modest price.
$700-$900 seems unreasonably high.
What is "current retail"? How much a store will sell it for? I don't think "current retail" means how much you get if you sell it or trade it in. Perhaps you can sell it privately, and maybe convince the buyer that it's worth $700-900.
That's their "Kelly Blue Book" value, not mine. There are sites on line with names like "price monkey" and "used price" that will quote you a price if you pay for a membership, but short of $100 and mint condition I would not be interested in that Mac.
According to www.everymac.com the estimated value is $700 to $900.
Similar to selling a car, it will very according to location, condition and extras.
I agree, it is high.
Apple and authorized retail stores stopped selling that model nearly 7 years ago.
Look on Amazon or eBay. What someone asks and what someone gets for it are not mutually exclusive.
Value of Like New iMac 21.5" Late 2009 Intel Core 3.33GHZ