Edit: Solved using custom validation with regex matching to ensure only numbers entered and then Piped Text for the comparison of values.

Hi there, I have a very similar issue. Is it possible for me to take a look at your code?

qualtrics_user_007 here is a snippet of the custom validation:
the regex I used for digits (since it's slightly cut off in the screenshot) was: /\\d+(,\\d{3})?(.\\d{2})?/ - this allows numbers like 1, 100, 99.00, 10,000 and so on.
basically the first two regex conditions ensure only numbers are entered and then the third line compares the two inputs and ensures the value in the Highest field is greater than that in the lowest field. I pulled the input in the Highest field as Piped Text for comparison.
hope this helps.