Can your blasters be modified or do they have to be stock? In addition, is there an FPS limit? Do the blasters have to be Nerf?

I terms of sheer price-to-performance, the BoomCo Dual Defenders pack is all you need. You can either A) Take the spring out of one of them and add it to the other for a single ~100 FPS blaster, or B) Buy a K26 spring, cut to length, and have a ~120 FPS blaster for you and a friend. Unfortunately, they don't use Nerf darts, but BoomCo darts are better to Nerf darts in almost every way - High accuracy, high stability, and usually low cost

If blasters have to be stock, the Rival Apollo is a decent choice. 95-100 FPS stock, moderately high accuracy, and they can usually be bought for $20. Ammo and extra mags aren't very cheap though

If you have an unusually low FPS limit (say <80 FPS) and/or you have to use Nerf blasters only, then any regular non-flywheel N-Strike Elite blaster will be fine, so long as you don't use stock Elite darts. Even the new AccuStrike darts are fine, but Elite darts are notoriously terrible.

The new-ish Buzz Bee Ultra-Tek blasters (such as the Champion or Snipe) should also be mentioned, as they get better performance compared to most Nerf blasters and can be bought for very cheap (as long as you buy them in-store compared to Amazon or something). They're even cross-compatible with Nerf darts and magazines. But, if you have an unusually low FPS limit or you can only use Nerf blasters, then the Buzz Bee Ultra-Tek blasters may not be an option.