Something under $500 that is relatively unbranded.
Better yet, look at a 29'er. Like this one.from Kona, Single speed, rigid, fat tire MTB. Run fat tire slicks, and it's a great commuter. The lack of shifting works well on flat ground, with the right gear choice (very personal decision), and the fat large tires roll well and comfortably. MTB durability means rough roads might as well not exist.
There are many bikes like this, and while i like the Unit 29'er linkd, I'm recommending the idea, not the particular bike.
As far as branding, that can be fixed with judicious use of tape, spray paint, and stickers.
I vote for a used hardtail mountain bike with 700c wheels and a rigid steel fork. If you put thin/ fast rolling city tires on there you'll be left with a quick bike that can handle some abuse and the upright geometry may make avoiding potholes and other obstacles easier. This is what I ride. I consider the 700c a poor mans 29er.
For daily use on Toronto roads (occasional but not continuous pot holes) I'm happy with a bike which has no suspension, strong wheels, and 700x32 tires (with tread but not studs) inflated to 80..95 psi.
Tires that wide might (? check this ?) need disc brakes, which are relatively expensive: so slightly thinner, XXX-28 tires might be cheaper because they can be used with cheaper brakes.