I picked up my 65-5 back in 2012 from SOSS for the princely sum of $339. I figure it's worth at least twice that now.
I also have a 64-5 that was re-barreled in 2012. It was a round-butt 4" heavy barrel originally that cost around $250, and I found a 3" barrel on-line for $165. I picked up the barrel before finding the 65, but I went ahead and had it done anyway. Even as a frankengun, I still value it around $550.
Finally, I have a round-butt Model 10-10 that was one of the repatriated Australian guns from Bud's. A short while back, I picked up a 3" blued barrel on-line. When I finally took it to the gunsmith with the 10, he discovered that the barrel was really for a .357, even though it was marked ".38 Special." He put it together with a recessed .357 cylinder he had in his parts drawer and it worked perfectly, so now I have a 3" model "10/13" to round out my K-3's. All together I think I have around $450 or so in it, but I don't think I'd go below $600 for it.
Almost forgot: I have a couple of those $149 barrel-less K-frames from J&G waiting at my FFL, and a pair of barrels in my drawer ready to put on them. I think I'm obsessed....