J.M.
Did you parents state what they wanted to spend (give you a specific budget)? If they did, and you've exceeded it, then they are not really obligated to pay more. any extra will need to be provided by you. If they did not, and you are being reasonable in your expenses, then it sounds like there needs to a little more communication in what you need or have done. Sit down with what you have and see if they agree or not. If they don't see how you can modify it. And be open minded about it. REmember, their putting up the dollars, so when it comes right down to, they get final say as to yeah or nay.
In the past, the brides family did pay for the majority of the wedding. I don't know if you in-laws are from than time period, and maybe just aren't aware that anymore it can be very equal. Typically, the rehearsal dinner was provided by the groom's family since the wedding was for the most part done by the brides. Sit down with them discuss what their expectations are and what you and you groom's desires are. If you go in with a list then you can modify. They need to expect to participate financially some as he's there son too.
Not living near where you're getting married makes it much harder for you. But with good notekeeping and communication you can do it.