I would suggest a used Nikon Earth and Sky 15-45x60mm. They are discontinued, but are a VERY good scope for the money. The come up on eBay pretty often... lightly used to NOS usually sell for $150-200.
The Leupold Gold Ring Compact 15-30◊50mm is another really good optic, but they are closer to your $400 max. Stay away from Leupold's Green Rings... you will be disappointed.