A lot depends on how steep the hill is, and how much riding you are already doing, because the biggest hurdle for bike and rider will be to tackle that hill every night.

700 feet in a mile is a 13% grade for 1 mile. Most new riders will not get up that grade on anything short of a mountain bike with that kind of bike's typical 24 x 32 x 26" low gear. No matter how ideal any other bike might be for the "rest" of the ride, walking a mile makes a bike undesirable in my view.

I would:

1. Go on Craigslist and spend $100 on an old '90's rigid mountain bike (MTB). They are plentiful and cheap. Get a good quality machine from a major brand. It has to have triple chainrings in front with the smallest 24 or 26 teeth, and in rear the largest cog has to have 32 or more teeth. It also has to be the correct size for you. Post some CL links that look interesting for people here to comment on, and post if you're not clear about sizing.

2. Spend $80-120 for a full service at a bike shop, they will go through and replace cables and pads, grease bearings, true wheels, adjust shifting and headset, etc. Optionally, replace the knobby tires with slicks ($50-ish).

3. Buy a good headlight and taillight. You're going to be riding near midnight, so this is mandatory. See threads here, there is one that has just started, in which I linked to a $25 light on Amazon that is as good as something you'd spend >$100 for in a shop. Also attach a red blinky to your helmet. You may spend $80 on lights, and it is well worth it. Also buy $10 of reflective tape and stick it on the bike, your helmet, your backpack, etc.

4. Buy a decent helmet (they aren't expensive, $30 could do it).

5. Buy a U lock ($25-40) and find a good place at work to lock up your bike. The good thing is an old MTB is not usually a big theft target. The bad thing is at 11 pm, everything not securely locked up is a theft target.

6. Finally, spare tube, patch kit, tire levers, mini pump ($40 or so all told?) and practice changing a flat tube. At midnight on the side of the road is not the time to learn.

Absolutely do not get a new WalMart type MTB for $250 - the twenty year old MTB is a far better bike. Do not spend up for a new bike until and unless you know for sure that you can handle that climb on it. The cheap old MTB will tell you what gearing you need, and at first you will probably need its ultra-low gearing.