you are correct:  Registry of Deeds or Grantor-Grantee Index as appropriate to the county.  In California, the State's Public Utilities Commission maintains many records for older utilities like railways, but tends to be less than helpful or open about providing access to the records, and mostly the matters of interest are in the County Offices and not at the state anyway.

 Pricewise, keep in mind that most large institutional clients using you for this sort of service on a regular basis will prefer a flat rate over a per lot charge.  In which case, ask for a bit of time to "sample" the work load.  Some clients will process the simple 5-minute projects themselves and leave only the crap work wherein exist indexing errors or  very old searches.  

Also, despite my last post, keep in mind that the cell tower rights may be within the past few decades, but utility access may rely on much older easements going far back in time.   This can easily add time and labor to a project that looks easy on the onset.