How far is the plate from the sensor? Another option would be to use a Sharp IR sensor, which you can get for about $10 US. They are quite accurate to about 3m, and can output distance either as a voltage or as a bit stream.
As far as ultrasonic sensors go, take a look at
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for parts. They all seem out of your price range, though.
I managed to obtain some ultrasonic transducers from
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They were cheap, but you'll have to build up a circuit around them to do the distance measurement. There are various circuits for this published on the web.
Regards
I would like to measure the movement of a 4x4 inch steel plate as it moves
> towards and away from an ultrasonic sensor.
>
> The basic idea is to have the ultrasonic sensor pointing directly to the
> flat 4x4 inch steel plate. The plate would be moving around 2 feet towards
> and away from the sensor.
>
> I don't care about the accuracy of the device; all I care is about the
> repeatability of the reading.
>
> I would appreciate if someone could give me a link to such device, I would
> be needing around 60 of them so a cheap sensor would be best (under $25 US
> dollars if possible)
>
> I appreciate your help.
>
>