I am pretty paranoid about my bikes getting stolen or messed with. I generally don't ride anything worth a ton of money for that reason to commute with. I'd say $300 is probably what my most valuable bike I commute with is worth including lights and other accessories. If you will always worry about your bike than buy a cheap used bike a good lock and you should be totally fine. If you don't want to add to your stable of bikes than just get a good lock as it has been suggested here and don't worry that much about it. Your bike isn't super expensive and its probably going to be ok. As others have suggested you may find some help from your job to lessen your worries. People lock up much more expensive bikes all kinds of places and are fine. If you start riding to work you will probably find lots of people will being looking out for you.