You can build one for less than $40.
I brought a 24x24 3/4" stainless steel expanded metal, cut it in half with a dremel then bolted together forming a ring. Then I bought some stainless steel zipties from Homedepot and bolted to a 18" weber grill.
Put some feet on it and you are good to go. no fuss no muss.
Proud Owner of a UDS & Kent double grill