Possible bladder stone...xray or ultrasound?

Another of MissKalamata's ignorant questions....

My vet recommended an x-ray for my cat, who may have a bladder stone. Some people here have mentioned diagnosing stones via ultrasound. Is it an option? Is the x-ray better? I suppose ultrasounds are more expensive, but how do they compare medically? (Silly of me, but x-rays just sound more ominous!)

And in general, does the cat have to do anything special before the x-ray/ultrasound? Forego water? How much does it cost?

Ultrasound is much more pricey (I think when I was looking into it we were talking $100 for 4 x-rays, but $500-1,000 for ultrasound?? - granted I had to go to a larger city, different vet for an ultrasound).

Bladder stones may or may not show up on x-rays. My vet does the x-rays, if nothing is seen & he still suspects it he considers ultrasound.

The ultrasound is better but it does cost more.
My cat had bladder stones and a thickened bladder with ecoli infection.
They were disolved with food.
My sisters cat had oxide stones and he needed surgery.
You do not need to prepare for the test at all.
It is pretty was.
They put like a el on the cat for the ultrasound.
I paid $150 I think.