You can theoretically use a sniper rifle out of the box, but you'll likely be outranged and outgrouped by any other sniper at the skirmish who has been at it a while. My A&K SVD is not bad as standard, does nearly 500 fps right out of the box and is pretty accurate too, so I'd probably get some kills with it as it came, but there is a reason why there are a crapload of upgrades available for it and every other airsoft sniper rifle. Either way, you are gonna need a decent scope on whatever you get. You can get a decent PSO-1 airsoft replica sight here for fifty quid if you go with the A&K SVD, although it does require a bit of coaxing to go on the A&K's rail:
http://www.ebay.co.uk/itm/270951265654?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
The A&K SVD can be had for about 130 quid, so that would still leave you a score under 200 quid for something half decent with a good scope on it. I'd expect to throw another fifty to seventy quid at the thing in upgraded bits and bobs to get it up to snuff for some serious sniping, and probably a bit more if you decide to really do a nice job on the thing. There are plenty of dedicated forums kicking around for upgrading A&K SVDs, a quick search on Google will turn those up for you. If you do go with the A&K, you definitely want the larger cocking lever, as the stock one is a bitch to pull back with cold hands, and a bipod is virtually a necessity for a sniper rifle too, unless you want to do the cliche terrorist 'bungie chord around a tree' trick. At least with an airsoft sniper rifle, you don't have to piss on the ground in front of your firing position to prevent the muzzle blast kicking up dust and giving away your position lol, but you almost certainly will have to Ghillie it up a bit, although that is an easy DIY job.
Keep in mind however, that any serious Milsim will probably insist you are on the rebel or Soviet side if you have an SVD, similarly, they'd probably insist you were NATO if you had an L96 or a Barrett, although for a regular skirmish, you could go on either side, but it is something to bear in mind if you have any plans to do Milsims, because to be outfitted for either side would probably end up getting expensive what with you needing an NATO and an OPFOR sniper rifle, and relevant secondary weapons too, not to mention the outfits as well!
As it stands, most stock sniper rifles are more like DMRs with a slower rate of fire without the upgrades, especially the A&K SVD, because the real SVD is semi automatic. If you want to go DMR, the WE GBB M16A3 is a good starting platform.
On my second game I could shoot one guy, and then gradually I became better and better. I'm still not good.
