Unless you are moving the grill a lot I would not worry about the plastic caster wheels. I have used these and they have been working fine. The pair for $7.
https://www.amazon.com/exec/obidos/ASIN/B001HYY0L8/tvwb-20
Stefan;
Good price! I do move the grill around a lot though. I grill all year round, so from November through April it's in my garage and I wheel it out into the driveway and then wheel it back in after cooking. The rest of the year it's on a patio in a corner when not in use and then wheeled out to use.