So I have a range of values 0 (low, left end) to 1500 (high right end) being controlled by a 0-1 fader run through autoscale. How would i reverse it so that 1500 is low, left end and 0 is high,right end?

[expr -1*($f1-1500)] should do it.

(which is equivalent to 1500 - $f1)
you can also do:
[swap 1500]
| /
[- ]

or
[1500 $1(
|
[- ]

hah, next time I will reduce complexity, as you demonstrate sebfumaster!

You can also set autoscale to output the range in the direction you want, eg:

[autoscale 1500 0]

James, that was my first thought, however, it didn't seem to work. And yes, I did lock the sketch and click the [1500( and the [0(