RIGHT(string, number) will return a string. If you convert this to an Integer then you could setup an IF statement that compares the output to the range you want to exclude.
I am not aware of how to use a wildcard in Tableau.
Why not just use a simple Boolean: Int(right([code],3)) > 699 AND Int(right([code],3)) < 900
Thanks John and Naveen. I'm going to go with the Boolean, that works perfectly well. Just for my future reference, I'm assuming tableau formulas do support wildcards?