Rather than charging by the page, I have charged by the hour. It took me an average of 1 hour to transcribe 5 minutes of video.
This may take longer if the audio quality is poor, if the persons speaking do not speak clearly, etc.
Be careful not to underestimate your time and ask for a sample of the tape.
Transciption can take a LONG time. $3/page is much too low, as it would easily take you an hour to transcribe a page. I believe most people who perform this service charge per minute of tape.
Dubbing has hidden expenses: you have to pay for the voice talent (duh!), but there's the studio charge as well. This includes the time it takes to record the voice-over (and don't believe that it can be done in one take: there's a funny noise in the microphone, or the voice talent sneezes, etc.) as well as the time it takes to make sure that the tape is technically acceptable.
Doubtless the client will ask you to coordinate the talent, studio and other production-related matters, so make sure you get paid for that time as well.
Costs of studio time and voice talent vary from locality to locality, so you'll have to do some research regarding prevailing conditions in your area.
Hope this points you in the right direction,