As to your other question, if you want to keep it (I urge that you don't), then the price difference is typically about 40-50% less.
To give a comparison, a Saco or Maremont nowadays is worth about 50,000 on average, some higher, although a friend claims to have sold his for 70,000 recently. A year ago, a Kentucky Armory M60 sold for about 30,000. That's a reweld M60.
However, here's a catch. I'm not sure if Aaron M of Sturm is on this board, but he can testify to this. The reweld M60 market has been put into flux because about 8 months ago, a rewelded M60 Saco sold for approximately 60,000 on GB. The buyer probably did not know the M60 was a reweld, and the listing did not specifically say that it was a reweld. Upon emailing he seller, the seller said that he put up pics and that was his only obligation. I'm not sure if the deal actually closed.
So now bc of that sale, people with rewelded M60s think their rewelded gun with worth much more. I've seen private attempts to sell rewelded M60s at 50,000 a few months ago.
Of course, any item is worth what people will pay. But there have been very few M60s up for public sale, rewelded or not, so it's hard to know what they're really worth nowadays.