People ask all kinds of prices for Peugeot PX 10s on eBay but that doesn't means it's worth $700-$1200. $400 +/- $50 is about right assuming that it's in decent condition. So you did fine and it's a great bike. But we can't value it obviously without the pics and you will need to overhaul it and fix it up before riding it.
Last edited by bikemig; 05-17-19 at 10:11 PM.