thats a 24/47 yugo mauser. In that condition its worth only about $150-200. the reason that is has a "good" bore is because yugoslavia never lined their bores with anything, and they shoot corrosive ammunition. I'd watch out with that one.
The mosin is going to be around $90-100 it appears to have a hex receiver, but if it doesn't that means it's just some re-worked factory frankenstein as was common for surplus rifles. And the battle of Stalingrad was just one of many fights going on at exactly the same time in a country that is larger than the U.S. I highly doubt that it was in the battle of Stalingrad unless it comes with proper documentation stating such. (these tall tales are common among suplus rifle collectors).
The enfield is a #1 Mk3 and those are a bit harder to come by now adays. The "unusual" rear sight is the exact opposite of unusual. All #1 Mk3's have it. The seller is confusing them with a #4 Mk1 which is the common WWII variant. I would bid no more than $300 for that rifle. Again, I would suggest looking at the bore and action of the rifle, and make sure it functions smoothly with no corrosion or damage to the mechanism. I have examined several and some had what appeared to be binding locking lugs.
The US model 17 is the nicest rifle out of all of them. I would go up to $600 for that one. However, I would check the butt stock and finish on the metal before buying it. If it matters to you (I don't know if your a serious collector or not). It appears to have been refinished. I believe that the finish on the metal for this pattern rifle during this era should be slightly green. Also, the wood should show basic wear and tear, but this one does not. It also appears that the buttplate was colored the same finish as the wood (A mistake that many make when re-finishing wood on surplus guns).
The model 1400 the "jam o matic" as my grandfather says. My experience and information all points to this gun negatively. However, It is in good condition and I would make a reasonable offer of $200-250.