Good for under $250? There's not really. $500 is a more realistic starting point, plus performance upgrades to make it shoot straight, so another few hundred plus. Even still, most properly tuned assault platforms will out shoot it.
No one on here is likely gonna recommend something that won't work properly, so you're kind of SOL on that. Also, we don't tell people who aren't age verified how/where to get guns. Please read up on the forum rules. If you get age verified, you may find a deal in the classifieds here.
You should read this:
If you're serious about being a sniper, then look into something like a TM VSR G-Spec. It's a good place to start, but will need a few upgrades for sure. Just like all worthwhile platforms.