My response is not directly on point to your question. But here it is nonetheless! I own a stainless 650, a stainless 651 and a titanium 651, all of them manufactured in 2004. The fit, finish and reliability of all of them has been superb. Each one has about 300 rounds or so through them so far, and I have had no failures to fire.
If it was in good shape and passed my visual and functional inspection, I would buy it for $ 300. I would be thrilled if Taurus made a 650 in titanium.