Most counties on the Left Coast post their fee schedules online, so digging through the Google and finding it online might be a very worthy endeavour to undertake, so that you can send clients a link.  The State Government Code also helps, but in California, each county is empowered to set their own rates for these services as based on the State Code, so the Code itself does not contain the fee schedule and is of less help to the end client, than the local County posting.

Resisting a flat fee is the best, but if you do offer a flat rate, then be willing to counter with some additional adjustable fees like scanning fees, shipping and delivery fees, etc...  This is the type of business tactic that I prefer not to engage in, as it feels deceptive, but I do so with full disclosure to the client as to why I am doing it (i.e. the County copy fees may not be sufficient to be covered by the flat fees, so I need the leeway to charge more, otherwise you won't be getting the work). 

If ignorance of the law is no excuse, then the fact that Counties have codified their fees by passing ordinances and the end client should hence know this, yet they are still asking for an unfair flat rate, then I would suggest that the client, while attempting to get a good deal, may not be playing above-board to begin with.  This does not justify deception on the part of an abstractor, but it does suggest that we need to have paying clients and that we need to find equally creative ways of keeping such clients.  Harsh business climates call for stronger action.