The mill has been cleaned up, repairs made, and so on as you said in your opening statement, and the pictures you posted. That's half the battle dealing with a used machine is taking it apart, cleaning and replacing/repairing parts. I would offer him $3000 tops and see if he takes the bait. The most he will say is no. And probably come back with a counteroffer. An agreed price of around $3500 would be a sale to me if I was buying that mill. Everyone here will have their opinion about this, but this is my opinion.
I will say, the table looks like it has been remachined by grinding. Which in my opinion is not going to hold up very good. It needs scraping marks, just not flaking marks, to carry the oil film to keep the ways lubricated. Likewise on the knee cross slide too. The thing bugging me is, there is flaking on a surface that is not a bearing surface on the knee cross slide.
One thing I will say, Wells Index used Meehnite castings in all of their machine builds. The way surfaces are quite hard, in the high 30's on the Rockwell C scale, at least on my 645 mill. For all of the years of abuse mine went through before I got it, it's still in fairly decent shape. It is losing accuracy. A little scraping will fix it. Just not sure I want to at my age and for the stuff I use it for.