The original Canon 5D had a great image sensor in a fairly average camera body. Is claim to fame was full frame without the huge size,heavy weight, and $8000 price tag of what was on the market at the time. Prices vary widely on the 5D, most likely because the 5D premiered at $3400 and sold poorly, and the was dropped to $3100, and throughout its life span Canon offered numerous,and frequent price cuts, as well as several rounds of rebates. At one time, it was possible to get a new 5D for just under $2,000 with a combination of rebates and selling off the printer that came in one bundle, so sellers of the original 5D have widely different expectations of how much a used 5D is "worth".
There are lots of good cameras on the market now. The market changes quite rapidly at times,as new models are introduced and old ones are discontinued. You need to decide how much money you want to spend,and what you want the camera to excel at.