Know of any sites for quick, cheap or easy set design?

This is a hard question to answer without seeing the script, and knowing how much $ you have, but here it goes.. Take a minimalist approach, and don't have a set. Have a black background and floor, with wings on stage left and right for exits and entrances. Use small items and light movable pieces that are easily and quickly carried/pushed on and off stage: For the streets of Agrabah (sp?) you could get two light moving carts and drape cheap, distressed fabric, (Get it wet and drive over it on a dirt road, heh..), over the cart. Get cheap baskets from a thrift store, and put them on the carts. Have extra bodies in as authentic looking costumes as possible, (Contact the nearby community college drama dept for inexpensive costume possibilities), wandering the marketplace and muttering to eachother quietly under the dialogue to add ambiance. You can embellish it with lighting also: Spotlights, (If possible), during intimate moments; and red and blue lights during heated moments, etc.. Sound is also a great way to add atmosphere. During a magic carpet scene, you could have a wind sounds and maybe even a little flute. Most importantly, great acting and directing can cover almost any flaws a show might have, and on a minimal set, the actor needs to work harder to help the audience experience the atmosphere.

It all depends on how many dedicated actors and tech people you have to help you carry out your ideas. One last thing, add humor wherever you can, your audience will thank you for it.

Maybe get the participants involved in the project to pool their creative energies to pull off the production.