Pedals are one area of your MTB set-up where spending more doesn't necessarily equate to a better product, though it it does tend to get you more choice. More sculpted bodies and improved axle material can reduce the weight, but generally also increase the cost.
It's worth noting, however, that a more expensive or complex MTB pedal won't necessarily be more reliable. In fact, Shimano's cheapest pedals tend to outlast pretty much any pedal from anyone else, despite sometimes being sold for less than a spare pair of cleats – which, coincidentally, they come with as standard.