How fast can I find an affordable folder? - very fast.
How fast can I find an affordable fast folder? - very slow.
How affordable can I find a fast folder? - not very.
How do I make an affordable folder fast? - pedal harder, become fitter.
How affordable are fast folders? - what's your budget?
How fast are affordable folders? - how steep is the downhill?
Sorry. It's Friday afternoon here.
[edit] Xootr Swift. Quite affordable, quite fast.
Second the Xootr Swift. Great budget mid-range bike.