I find that used Mac prices vary widely by location, and even between cities in the same state. Because of taht I feel the community sales option Bob recommends the be the most effective way to see representative pricing.
Example: I live in a town that, until Costco started selling Macs recently, had no Apple resellers for computers. However, 30 miles away are two university towns, with each university selling Macs.
When I compare Craigslist used Mac pricing for the Uni towns, the selection is far better and the prices about 10-20% lower than where I live.
✋🏼 TIP: Before you sell on your Mac, be sure to carefully review this Apple support article:
What to do before you sell, give away, trade in, or recycle your Mac - Apple Support
We see a lot of posts from angry buyers here when a seller does not properly prepare the device for sale. You don't need an unhappy buyer showing at your door!