Rehearsal Dinner

The groom`s parents have not shown interest in helping their son with any of the wedding costs and/or rehearsal dinner. They are not happy about the marriage because this is their only son and for some reason they don`t believe in marriage. They like my daughter but just don`t seem interested in the wedding or wedding plans.

My question is this, what do you do about a rehearsal dinner when you are paying wedding on a budget and don`t have the extra money to have the rehearsal dinner? Is it proper to just not have a rehearsal dinner even if you are still having a rehearsal?

What should we do??