White dialed 6138-8000 or 6138-8020s are averaging closer to $800 (many sellers asking $1000+) I know that seems high but that’s the new norm. When I went to get my Snorkel 666 serviced that watchmaker said “the service price is worth more than the watch” He still thought they were selling for $100

 

I'd say if you get a good Panda for <$1000 you're doing well, especially if it's on a correct bracelet. If you're buying a 6138-8020 for $800 or less, then either you're very lucky because the seller doesn't know what it is, or there's something wrong with it. Most of the Pandas on eBay have fake dials and/or other problems.

I had this pair a couple of years ago:


The one on the left has a non-original bracelet (it is a Stelux Seiko but had end links modified to fit) and had been polished in the past.
I sold it on eBay to a guy in the US for a little more than £1,100, which is about $1,300 in today's money.