I too have a hankering for a 28 ga. I hear nothing but good things on them. I'm really leaning toward a Browning citori. A bit more than the $500 you had in mind but the more inexpensive O/Us don't fit me too well.
I have two Baikals in 12 ga SxS and they fit good. and are well under $500. I have to look and see if they make it in a 28. If so, that would be my choice for the price you're looking at.