The Sig P250 is relatively new, maybe 3-4 years since being released.
Interest in this gun has been very tempered, hence the bevy of brand new guns available for under $400. That's a couple hundred bucks below where they began, as I recall. I shot one and didn't like the trigger. Just generally didn't like the whole gun to be honest. But as far as function they're supposed to be pretty darn reliable.
Here's why I think the price has been reduced:
The Sig enthusiasts prefer the established and finely finished alloy models, so they swung and missed with that bunch. The Glock/XD/M&P crowd already have a polymer they like, and it's got a better trigger and more common parts and accessories than the P250. So they've found themselves without a strong target group, and have gone the Taurus route with these models (lowering prices) in order to pull in first time gun buyers and younger shooters. And by most accounts, it's probably not a bad gun for a newer shooter.
"The Future is Unwritten"