A few years ago I came across a wonderful resource from the Archdiocese of Cincinnati. I'm glad to see that they're still providing this service: Cincinnati Archdiocese Record Archives
For $25, they will do up to 1 hour of research and provide copies of up to 10 records. A sample request letter is provided here: Request for Record Research Be sure to read the other info on the links to the left.
I requested 10 baptism, marriage, and death records and received a nice response back, along with copies of the records. For the records they did not have, they provided a reason. Out of the 10 I requested, I received 8 records back. One had been destroyed by fire and one was too recent. They said they had a strict policy of not sending records out from 1920 on.
The copies I received were for an entire page, so I lucked out and found some other family references on the same page. A transcription of some of the records I received is here: Mercer County Ohio Records