Ignore the stuff about all of the time gearing up. That's not necessary unless you have a really long commute like 20 miles each way or want to imagine yourself Lance Armstrong or something. Regular clothes are fine and that's what I wear for even 10 or 15 miles each way. I've ridden in Prada suits and even a tux a couple of times. No special shoes, gloves, helmet, etc.

As others have said, just about any bike will do. A city bike would be ideal though likely difficult to find for $700. Something like a Bobbin, Breezer, or similar might be a good option. External derailleurs add complication, maintenance, and grease on your pants so a single speed or internally geared hub would be the ticket. Avoid comfort or flat foot bikes like Electra though unless you like back pain.

BTW, I bike 1 mile quite often. 5 minutes on my bike vs 20 walking, easy decision. Actually, I bike a bit over 1/2 a mile quite often to a local pub.