In addition to the $10 per signature a mobile notary charges to notarize a document at a California jail, prison or detention center, mobile notaries also charge additional fees for their services, such as travel fees, etc. 

For instance, at the Pitchess Detention Center in Castaic, California, they allow notaries and attorneys only during the weekdays. If the inmate's original photo identification (such as a driver's license or passport) is available for the notary to examine, a notarization can be done during a weekday for a lot less because the notary can usually get in and out within an hour. 

However, if the inmate's photo ID is NOT available, then two credible witnesses who have IDS and can positively identify the inmate can go into the facility with the notary on the weekend and wait in a long line for at least 3-4 hours.  Of course, this will be more costly.  Note:  The two witnesses who may be used cannot have an interest in the transaction or be named in the document being notarized.

Using a notary who has years of experience, has performed numerous notarizations at prisons and detention centers, knows the best times to visit, and is familiar with notary laws, will save a lot of time, frustration and money in the long run. 

It's better to get the job done right the first time rather than finding out later the document that was notarized is invalid and you have to pay another notary to go back and do it all over again.