Sara, basic lookups in the online version are free. They'll tell you the year and the parish where the records were recorded. The subscription is a little bit of a pain, because you have to set up your account online, then call them the next day to fund it over the phone. I'm lucky enough to have a major reference library downtown which has all of the PRDH reference books (they're huge and take up a whole shelf, but I have the luxury of perusing the entire parish record for everyone in the village at the time.)
I believe the online version charges you just a little bit for each hit where you're looking for the entire record. (With conversion rates, it's about $11/150 hits.) But then, once you establish the parish and year, most of the info's already online in other sites (like familysearch.org).
The other option is that they have all of their materials on CD now. It's expensive (abt $580), but if you want a great tax deduction ;-) buy it and donate it to your local library...then you'll always have it available.