PTR Record probelms

I have a problem with my mail server. We are currently using MS Exchange 2003 standard hosted on our server, and we have a problem delivering e-mail to some domains, e.g. AOL.COM. They claned that we do not have a PTR record. We tried to corrrect this with our ISP,but our ISP will not do any valid PTR reverse records unless we have a bussiness account with them, which starts at about $200.00+, any body has another idea how to fix this?