The way I figure if you've a pretty nice bike (let's say $700+), you might want to have a Krypto NY chain + a decent Krypto U-lock which is $90-120 worth of locks right there.

If I was going to be leaving a bike out in the open for 2-8 hours at a time I'd just cruise CL/thrift shops/yard sales for a crappy second bike for those commutes/errands. I've found some pretty decent 90s rigid MTBs for $10-50 around here. Then just lock that up with a $30-60 lock depending on the neighborhood. I'm guessing Cambridge, MA? I've heard Boston area is pretty harsh for bike thefts. If you go the cheap bike + decent to excellent lock, you're only going to be out $40-110 when it gets jacked instead of $730-820.