What is a good airsoft sniper rifle for under or around $100?

There are multiple good ones out there, unfortunately there are none that fit your price range that I know of that supposedly are decent quality guns. You can look into L96 style rifles and you will probably find one that will fit your price range. I've heard Well makes a fairly decent gas sniper rifle. I'd recommend spending at least $150 on your rifle to get a fairly decent one. I know of a gun by Echo1 called the M28 which is very good for its price, you'd need to downgrade it though seeing how it shoots at 500fps. Also, just about any stock retail gun you get will shoot 500+ feet per second with a .20 bb. You'd end up downgrading the spring probably (unless you use a gas gun in which case it should hopefully already shoot at 400fps or so) in your gun, which isn't very difficult, but would have to be done to make the gun field legal( at least at most airsoft parks). I'd recommend looking at your local craigslist postings and seeing if your able to find anything there. Always research a gun before you buy weather you get it from a retail store or non-retail provider. Some good retail websites to look at would be Airsoft GI's, Evike's, and Airsoft Megastore's. I believe all of them will have rifles that will fit your target price actually, but the only issue will probably be the fps. Hope this helps.

The M59A Features: Push button clip release holds 30 BB’s Full 1:1 size sniper rifle with real bolt action Heavyweight metal alloy core construction with durable plastic housing Extra long, one-piece aluminum barrel design for extreme accuracy Adjustable hop-up for more accurate firing Includes 50-pc. 6mm BB's, speed loader, and shoulder strap Length: 39" Shoots at 450 FPS with .12g BB’s

The M59A Features: Push button clip release holds 30 BB’s Full 1:1 size sniper rifle with real bolt action Heavyweight metal alloy core construction with durable plastic housing Extra long, one-piece aluminum barrel design for extreme accuracy Adjustable hop-up for more accurate firing Includes 50-pc. 6mm BB's, speed loader, and shoulder strap Length: 39" Shoots at 450 FPS with .12g BB’s