I see one on P&s militia collector for $550
M38's, not K31's I take it? Interesting that you came to those as your choice; those were the exact two I chose as my favorites for a long range, accurate military surplus rifle. I was eyeing all the K31's in the stores last year while waiting for my PAL. My application was delayed, and by the time it came through, there wasn't a one to be found anywhere in stores. I bought an M38 as my consolation prize. Got a nice example, mirror bright bore, though with a small crack in the stock by the tang. Have been watching the EE like a hawk, as well as other forums. It's taken me about 4-5 months of effort, but I think I have a K31 now, due to pick it up this weekend. Don't want to count my chicks till I have it physically in hand, but I'm hoping I have one now. Really excited about it, and can't wait to see how it shoots. Once I have it in hand, I might be willing to part with my swede. It's a true M38, purpose built, with a turn down bolt, and not a converted 96/38.
The price on k31's has really gone up since the stores ran out. They were $300 in stores, but on the EE I've seen them anywhere from $500-1200. I'd say that right about this moment, if you see one in the $500-600 range, that is a good price and worth snapping up, as the value just seems to be going up.
Big difference I noticed between a K31 and an M38 is the ammo cost. GP11 is on clearance at WSS for about 65 cents a round. Cheap PPU 6.5 swede still runs more like $1.25 a round. That alone makes a K31 a good value. Take into account that GP11 is reputed to be a match-grade target ammo, and that lines up to be a really sweet deal.