Mutually exclusive terms. Least expensive would run you 2500 or so.
Yes
Buy the one YOU like.
Buy a decent sniper rifle (gas or spring) a scope if it doesn't come with one and then practice.
Yes you can put a bipod on any rifle.
Yes. Most sniper rifles are based on commercial designs, and mil-spec variations can be purchased.
Parade store site. $160
you will never go wrong if you buy the best you can afford
There is no most powerful airsoft sniper rifle that you can just buy. But, Iv'e heard of guys tuning them over 800fps with custom parts. My most powerful is 600fps.
they have one for 70 bux at airsplat
You can never go wrong if you buy the best you can afford, regardless of the maker.
try crw-airsoft
You must be atleast 18 to buy airsoft guns and accessories.