I found a cheap, simple cupholder at the dollar (100 yen) store in Japan "DAISO". I like this solution because you only need to "install" it when you have rear seat passengers who need a cupholder. For me, that's pretty rare but I'll still keep a pair of these in the trunk just in case. Note: if you have European lock knobs, don't lock the doors when this cupholder is in use! :O
