What equipment are used in mountain biking and the cost of the equipment?

Well, there's a bicycle, hopefully a helmet, maybe a pair of gloves. After that, it all depends. The hardcore downhill crowd tends to be kitted out pretty much like hockey players, knee pads, elbow pads, back protectors, maybe even shoulder pads.

The cross country crowd are usually satisfied with helmet, gloves, tight fitting jersey and cycling shorts.

Inbetween are those who'll chuck a helmet on and then head out to ride in jeans and a t-shirt.

The cost can be anything, from maybe 300 USD total, if you're buying used, to 3 000 USD for the bike alone.