Here is a pretty good low cost solution for you from Academy Sports. I have a set of these and I use them on my kettles. I switch between these for high heat and my normal Weber grates when doing low and slow. I like that I can use them for either the 22.5 or 18.5 inch kettles. Better jump on it quick because I just noticed that they are on clearance.
WSM, 99 & 09 Performers, 2-OTG, SJG mini WSM, Summit 420, Q100, Akorn, and Schwenkgrill