Like he said. It's what your willing to spend.

For squeals, I'd go with the MXR Wylde Overdrive, or the cheaper Boss SD-1.
YOu can get single pedal octavers as well. YOu could get a cheap boss, or and expensive electro-harmonix one.

Or if budget is a problem, look into a digitech rp-80 multi-effect. Not the best, but cheap.

I'd personally go single pedals.