I really, really advise you to hold off getting a sniper. In airsoft, they're very, very ineffective. They have (pretty much) the same range and accuracy as any electric, and unless you spent just about every weekend of your first 15 years of life, every weekend, in a forest, you're not going to have any idea how to effectively hide with 3-d camo.
The biggest problem with single-shotting people in this is.. people go by sound most of the time to tell hits. If you hit someone in their vest while they're firing their gun, 99% chance they're not going to hear you. The point of sniping is lost in airsoft technology. The way it's (kinda) supposed to be is: Poof! Phil's chest just imploded. The bullet was launched from 600+ yards away, and the longest reach your guns have is at best 400 yards. It takes a very long time to run that extra 200 yards to engage, especially engaging an invisible target who's probably packed up and gone before you manage to find where he shot from.
Airsoft sniping is more of.. hiding and praying. There is NO 200 yard dead-zone to buff you from other people's attacks. Everybody has a faster, lighter, automatic gun. You end up with a backyard-plinker. The only advantage you have is camoflage, and unless you're a former military sniper or an experienced bow-hunter, you're boned in that category.
I've got two sniper-grade guns:
ARES L96 lightly upgraded.
Classic Army M14 (Match) Stock.
The L96 can put a .40 round onto a torso-sized target easily at 70 yards. Killshots are possible from 110 yards+. And, it's .Completely. Silent. It's not like ben's TM VSR-1. No screaming BB's, no muzzle wash, nothing. Just the click of the trigger spring is the loudest part of the gun. Bad side to it is, fully loaded it weighs some 17+ Pounds. Perfect gun for good, old, CS-style camping. The guy who I got it from spent at least $850 to get it all together.
My other gun that's sniping capable is a CA (Classic army) M14 Match. It's completely stock. Most people think of the CA M14 as just short of an insult with a trigger, because it's hard to upgrade and it's internals are unique. You're stuck with the stock the gun comes with, be it EBR or Match. But here's where most people forget... the CA M14 is one HELL of a weapon right out of the box. It's got the same range capability as my upgraded ARES rifle, with .20 ammo. When the gun is fully upgraded with, barrel, spring, hopup, + some other bits, 110 yards is a pretty acceptable range for taking accurate shots. And the best part is, it's automatic-capable! Meaning your baddies don't have just one 'pop' to listen for, you can hose them from waaaaaaay over there.
If you're willing to spend a good chunk of cash on a gun, I'd say buy a CA M14 off of AirsoftGi. Or more cost effective, a JG G3-ST1 (With the built-in bipod. I had one of these for a little bit, it's almost as accurate as a CA M14), or an AGM 614. And just practice with a ghille suit at games (I'll gladle help you make one), but just remember - the shadows are your friends, and a Chewbacca suit doesn't make you invisible. After you get a lot of practice with a ghille suit, get a nice little .22 LR to practice shooting with, (Not at games), and maybe ask ben a question or two about his VSR-1. Cause that thing is scary awesome. And he makes it even scarier, he's got some real fielding skills.
http://www.airsoftgi.com/product_info.p ... ts_id=3821
http://www.airsoftgi.com/product_info.p ... ts_id=3025
http://www.airsoftgi.com/product_info.p ... ts_id=2570
And, as far as scopes go, it's airsoft. You don't really need a scope for anything under 400 yards. Get something with good sights built-on, and keep a pair of binoculars near.