Ignore the naysayers. Body armor is cheap insurance. I wore a vest while working at a bar known for bad problems. Yes its hot, but manageable. Wear an Underarmor shirt underneath and you will be fine. Vests arent always noticeable, you can dress around it. Or be like Junior on Reno 911 and wear it outside your work clothes,
Second Chance, Point Blank, and Safariland are three manufacturers that I would trust. At bare minimum a Level II would suffice, but a Level IIIa is great. Trauma plate is a tossup, maybe you need it, if you are facing people with rifles? Theres more options than just a steel plate, do some research on it through the manufacturers.
Get fitted for a vest, so you know what dimensions you will need. You can't simply go by the S-M-L-XL-XXL, as that typically only addresses the chest diameter. You also need to figure in the length of the torso, both front and back sides.
Once you know what size will work, (its okay to get it too big around, so you can overlap the coverage) check ebay for vests. There is a 'born-on' date on each vest, so make sure you get something made in the last year or two.
A quality vest brand new can easily cost over $1,000., but when buying off Ebay expect to pay about $250 or so.