I would say the rust on that tan one has progressed far past than what has on the green one. The wheel well is gone the core support is gone since the bumper is pointing skyward and the rockers are gone too I would assume since the lower side plastics are aiming down at the center where the doors meet.
$3900 usd for a 29 year old vehicle on jack stands with the front end taken apart and needing roof repainted, with some potential rust problems does seem a little steep to me. Then again it is a hightop conversion van and having the front off and no lower plastics allows for better inspection.
I would investigate the rust on those upper dutch door hinges a little more. Check and make sure the rockers and rear wheel well arches aren't starting to rust. As for the core support, check how bad the rust is, if the owner will let you (which he probably won't) tapping at the rust with a pick or pointy screwdriver will let you know if it rusted through or just surface. I haven't seen very many that didn't at least have surface rusting around where the metal over laps are at those two points but if it is just surface rust, you can slow or prevent further decay by cleaning it all up and treating it with a rust converter type of product. If it is rusted bad enough that it is starting to have holes in it, then if you can find a pristine one to replace it with you can drill out all the spot welds and install a new one, only needing to do spot welds. It is actually an easy and fairly quick job if you can find a replacement. The other option is cutting out the rust and welding in whatever, tubing or patch panels to fix it.
google says there were between 3.2 and 3.7 million astro/safari made during their entire production run. So there are alot of them out there, though less every day, this one does look worth saving, but it is 29 years old.
For reference I paid $3500cad for my 03 awd, $1000cad for my 01 rwd, and $600cad for my 98 awd, and I don't haggle or low ball people, those were the prices for the first two, the 98 was asking a little more but he took his wheels off and the van wasn't running and full of junk. The 03 and 01 were in pretty excellent condition with pretty much fully intact core supports and rockers. The 98 was owned by a roofer who managed to damage every single body panel and the rockers and core support need replacing. None are hightops, though they all will be when I'm done with them. There are usually about 3 astro/safari cycling through the local wrecking yard I go to, so there are many around here and many getting scraped. Prices have come up in the last couple years like everything else, though a lot of older vehicle prices around here seem to be dropping off too. Local market and demand will dictate the price I suppose.