I you mean a cs500p echo, that is a pro built saw, split mag case, clutch driven adjustable oiler etc. and at 400, thats 50 clams below MSRP.
Just make sure the dealer puts a realistic H screw setting on it.
Stihl 290s, zillions out there, clamshell saw, homeowner grade, 150 used, etc.
Makita 510 dont know if that is a good deal or not
Of those three, most likely I would take the echo, . with that said, you could also look for like a decent used husky 346xp for in your price range and lower.
do you have any other saws?
If you look at other help me choose a saw threads, one of the first questions asked is, exactly what size and type and quantity of trees are you cutting? Just saying firewood and cleanup varies too much. I have had to clean up big windstorm and tornado downed trees..see? big ones... firewood can be six inch sapling clearing, saving the butt end logs, which I have done and used, to bucking up 40+ inch yard tree takedowns, which I have done and used.
With that said, I am more a fan of 60 cc class one saw plans if you are getting into larger trees all the time.