Folding bikes really run the gamut from too cheap to too expensive. My soon to be ex-BIL has one that I liked a lot, just can't think of the name. It was very rideable, easy to fold. Around $700 I think. I have tried the Dahon brands and they aren't too bad, but get the better of their models. I have seen the lesser ones and they got nasy looking. I think I would go for the stainless steel version they make for boating.
Camping World has a telescopic version I am unsure about. Looked like a good idea, but just not confident in the parts.
Best one is done by S&S machining, they make a quick disconnect adaption to whatever bike you have. That is procey, but you get a top quality machine. Not for an around the campground rider. This would be for a serious rider that wants no compromise.
Bike Friday is a good quality example of a folder. Not cheap but you can do real rides and real speeds. I have a Cycling Forum friend that used to take it with hiom on all his business tripps. Not a folder as you might imagine, but a transportable system. Have to reassemble, but it all packs into a suitcase. They make a Bike TwosDay that assembles into a tandem.