A local art club I belong to uses panels
from these people; one of our more ambitious members has made fitted fabric sleeves to pull over them for a plain linen-like background. We only use them for indoor gallery-style exhibitions, so we don't have any shelves, chairs, roof frames or other peripheral goodies. The price is not trivial, I guess you need to decide whether this sort of activity is going to be a regular thing or a one-shot deal. I've seen some covered booth-like assemblies with telescoping aluminum poles and fitted fabric flies and all, don't know who makes them, but am sure they're even pricier. Were it me (a cheapo) I might attempt to make some frames of 2x2 or 1x3 wood and fasten welded wire fencing over them. Hinge a few together with removable pin hinges.
Also plan in advance how you may deal with wind -- maybe ropes and tent pegs (and a mallet to pound them in with) -- as I've seen some pretty nasty conditions at outdoor events.
DaveT