This issue recently came up in another forum, and I think the inexpensive cloth shown in the OP's pic looks very good.
http://www.classicspeakerpages.net/IP.Board/index.php?/topic/10370-nla-grill-cloth/
http://www.classicspeakerpages.net/IP.Board/index.php?/topic/10370-nla-grill-cloth/






