Don't know of restrictions. Most are 3-4 legged variety. Don't know about cabanas, but would only consider them proper in far back. Ones with poles, frame, etc. are allowed.
No definitive answer as to decent. Ideally, it should shade, ventilate and withstand gale-force winds
Finding that, in combination with cheap, would be the holy grail of shade structures.
Keltys are by far the most common and very good if you're not vying for one of the first row shade spots. If you are, the downside is you block the view of anyone behind you as their fabric comes down to the legs. Personally, I don't like that and the fact they don't ventilate very well.
EZ UPs are great for view and ventilation, but are: heavy, bulky, pricey.
Personally, I like EZ UPs and old Coleman GeoSport Shades (which have been discontinued). Places to drive in stakes, anchors and tie-downs are good things, as you don't want it to become an IFO (identified flying object.)
Bad things to stay away from IMO are the cheap Walmart EZ-UP-wanna-be shades with fiberglass poles that form the canopy. Telluride winds will shake those poles down and up again real hard and suddenly you have no canopy, just frame.
Trolling local garage sales and CL has been very good to me...good luck.