I have never sought access or copies for a SP documents but have requested other documents where a charge has applied. I have done this on three occasions. On each occasion I forwarded a cheque for an amount to cover what I estimated it would cost and told the bodies that if it cost more or less they should contact me for the additional monies or refund me as was appropriate.
Depending upon how many units in your SP and the systems used to record the information you want, charges will vary I guess. If they are going to charge more you should ask for details of how that charge is made up. Asking them for details of how a charge is made up also puts them on notice that they can’t just pull a figure out of the air and the makeup would help if you disputed anything.