Ok, so I got an MPU6050 the other week, pretty happy with it so far. I see 400 microG per hertz as noise in the spec and I assume that's a one way to compare error between various accelerometers?! The lower the number the better. Please correct me if I'm wrong.
What's the most precise accelerometer and/or gyro below say $500? Or even something more precise, less erroneous then the MPU6050. I know there's filtering I can apply, DMPs, I'm simply talking in terms of raw unfiltered data.

Thanks!

Darn, I thought I actually put that in my original post. I need this to work high range. 100-150ft.
Everything I've seen so far in terms of ultrasonic sensors are limited to a few meters at best.

I need to be able to measure distance underwater between two points. So I'm thinking something as simple as a sonar should work. One sends a ping the other one receives it and replies back. Is this approach feasible? Can anybody recommend sonars I can use?

Thanks!