A sniper needs to be as quick and accurate as possible on the field. Every shot must count.
To achieve that, beyond being in an excellent physical shape, you will want a lighter gear than the regular assaulter. Last but not least, you'll prefer precision tools. A cheap electric smg might be light on the budget but won't help much because this kind of toys are poorly crafted and they lack any aftermarket parts whatsoever.
The best side-arm for your role would be a gas pistol with an adjustable hop-up. Try KJW, KWA Glocks and M9s.
Define "cheap"
"Best" requires opinion, "sniper" refers to how you use it, and "cheap" descries the user. Airsoft is a manufacturer. Please respect this site as the privilege that it is or risk blockage.
Want ad, pawn shop, department store
go for the m14, unless its cheap looking.
Most of the guns listed here will shoot around 400 fps or above. http://www.6mmbb.com/servlet/the-Airsoft-Sniper-Rifles/Categories Expensive guns are around $300-$800.
Probably the Cybergun Swiss Arms M6 Short Version. It's about $65 to $70. But I would go with a quality sniper over a cheap one. It'll last you longer and will shoot more accurately
See the related links for cheap airsoft guns.
What do you want it for? I've heard they're fun and cheap to shoot, but you can easily put an eye out, so it's important to understand what you think you're going to be doing with it.
it depends on what cheap is to you
I say twin ozez are the best cheap airsoft guns
Airsoftmegastore.com
You aren't going to find a "cheap" one unless $200 is cheap to you. Anyways go to Cobra Airsoft and the should have one for around that price