I agree with the 100' rope escape, but not because of the price. It is cheap, but to my experience, it's also the most effective. The reason is, when you have the audience tie you up they know that you're restrained. With handcuffs, there's always the thought that they're gimmicked (a frequent accusation regarding straight jackets also), or you have a handcuff key. With many of the more elaborate or impressive looking (to magicians) escapes, you have to teach the audience that it's a restraint, that it's dangerous, etcetera, and even then it's often little better than a vanishing/appearing lady illusion. Spirit ties are great and all, but they're either over too fast, or you have to work it as something other than a strict escape.
The rope escape is also versitle, you can be tied to a chair, a tree, a moving vehicle, combine it with any number of other escapes, on and on; and it can be done with different materials - extension cords, for example. It's also a good learning tool, because you learn to direct (or misdirect) people without them knowing it, which will help you in other types of challenge escapes, and because since it is so simple it teaches you to give a stronger presentation.