If you want a thumper, well my friend, you found it! I have not shot the 8mm Mag, but I did some reloading for a guy a guy at work who purchased a custom 8mm-06. It was one of the last guns built by a local gunsmith before he passed on. It had a "step-down" 24" barrel built on a mauser action with a Timney trigger and custom birch stock with a slight left kick. It is basically the most comfortable rifle I have ever held.
Anyway, this guy purchased without knowing that finding factory ammo is nearly impossible in our area. He heard that I reloaded, so he came to me. I did some load testing for it and found the 185gr Core-Lokts to group the best. I suggested maybe stepping up the bullet weight, but he said that he didn't want the extra recoil. I went ahead and loaded up about 300 rounds for him, enough to last him the rest of his life.
I have to say, after a couple of range sessions with this gun, I was sore!!! I can handle recoil farely well, but after running 20 to 30 rounds through it in a single session, it wears on you. If you do get the 8mm, it will be a gun that will handle everything in North America with authority. You could compare it a .338 WM, but with more "juice" behind it. This is the same case used on the 7mm STW.
As for price, it all depends. Is it blued or stainless, synthetic or wood, bdl or adl? I recently purchased a 7mm RUM CDL with a wood stock and "fancy" receiver and mag plate engraving, Sims recoil pad, 100 once fired brass, 40 accubonds, and die for a bit over $400 shipped. The gun is flawless and dare I say beautiful. If it were me, I would offer $275 and see what happens. If he agrees, you got a nice gun for a good price. You might feel a little guilty though, but he seems like he wouldn't mind getting rid of it.