I have a 505. Bought it from a used tool dealer for $150 with a brand new cord and brushes. In the near-mint condition it's in, I thought I got a good deal. I used to run these thirty-plus years ago in school wood shop, and they were bulletproof. I bought mine party for nostalgia, but also because they are heavy, solid and good for sanding large surfaces. They will put a really nice final sanding on something with 220 or 320 grit paper.
The one you show pictures of is pretty nice. I'd check eBay but they're up in the $150-$250 range easily. More if you have a case, a manual or anything else that came with them.