I highly recommend an E-Z Up canopy. And that recommendation does not come from just me but from conversations for the past 8 years with hundreds of other penmakers. Nothing else comes even close to be as popular or as highly mentioned. Also be prepared with anchors for days with the wind blowing. It does not take a lot of wind to move a canopy around. Buckets filled with concrete make great anchors.
A great way to find a good price on an E-Z Up is to watch craigs list for vendors that are retiring. You may also come across one through the grape vine at the market. Someone that just upgraded and is looking to sell there last one.
According to one link they start as low as $109 but you can also get all sorts of accessories for them.
Here is a link to one at Wal Mart
You can use them with or without the side walls.
Here is the link to the E-Z up site that will allow you to see all the models.
the other services that are available etc.
and that is just from E-Z Up themselves. lots of aftermarket items are made to work with the E-Z Ups.
Notice at the bottom of the links the Graphic service. You can get your banner or sign printed right on your canopy.