Industrial Design 101: From a UX perspective, you want useful things to be around when you need them, and to disappear when you don't need them. Occasional-use items that are bulky ought be designed to fold up or break down. The plastic folding sawhorses in my shop are among the most useful items in there.
I wouldn't have paid for them, however; they were given to me as a gift. Sawhorses are basic enough that you should always DIY rather than buy. You can make a simple pair of folding sawhorses with butt hinges, but if you don't have any handy, J.G. Dean's breakdown design is the way to go. His sawhorses are cheap, useful, quick to build and take up a minimum of space.
"I can't claim to have originated this design for sawhorses," Dean writes in his Instructable. "I've seen similar ones in workshops and on construction sites for many years, but I believe I've made some improvements in their construction and an modification/addition that makes them more useful."
These sawhorses are made of inexpensive 2x4 construction grade lumber except for some scrap plywood, and some screws. They set up and knock down quickly and easily to take up a minimum of space, and provide almost as much support for sheet goods as a large work table.
The entire system can easily be built with a table saw in under an hour for about $30 once the cutting jig is made out of some scrap wood. I based all the dimensions here on sawhorses that are 30" tall and 48" wide, which are both taller and wider than most commercial sawhorses.
Since the top edges of the cross pieces are often cut into during use, I've found that it's better to make them easily replaceable.With these, the top surfaces of both sawhorses can be replaced in minutes for generally about $5-6.
Check out Dean's full Instructable here.