$750 for bare bike is $1000 once you add lights, racks, fenders so I’d be inclined to look for a $250 used bike in good condition or $500 brand new. Reliability depends mostly on operator awareness. Riding on tires with half pressure, not knowing a headset, hub bearings and BB are loose or too tight. Not being aware brake and brake shoes aren’t adjusted correctly, etc. Not knowing how to adjust a derailleur so it doesn’t throw a chain into spokes. That lack of awareness can occur with a brand new bike with its one free check up so buying new is no guarantee of reliability if owner cultivates lack of awareness.
He might consider studded tires for road ice. I commuted in MD for a few years all year around and the excitement of ice just isn’t worth it. Sure they’re slower but the ability to ride up on an icy sidewalk while cars are sliding up behind you or not ski down to a stoplight is worth it. Studded tires can be $100 each depending on model.
You don’t mention gear needs but if it’s flat there’s nothing wrong with a single speed.
Either way visibility will be very important, lights on bike, lights on helmet, yellow vest or jacket, reflectors, etc.
Don’t get the cheapest tires but he doesn’t need the fanciest. There are lots of $50 tires you can ride through glass on.