I think the others with the eye bolt/hook in a stud is your best bet. It'll be the cheapest and least cumbersome, while being sturdy. A PVC frame is fine, but will be somewhat in your way and cost more than an eye bolt. If you have a tent frame like someone else mentioned, then that could be used at no cost.
Magnets work great for finding studs too if you don't have a working stud finder. Run the magnet over the wall until it wants to stick to a nail under the paint. There's a stud. Might not work in all cases, but of all the stud finders I've owned the magnet has always worked better. I should mention my stud finders were either free or on the cheaper end... but magnets are typically cheaper yet or free :)
I think some/most drywall anchors are meant to be used on vertical walls (not horizontal ceilings) and are rated as such. Just because some anchor holds 50 lbs on a wall doesn't mean it'll hold that much hanging from a ceiling. It's going to be pulling on different parts of the wall/anchor.
