Until there is uniformity of application of RESPA throughout all the federal circuits with respect to mark ups, you need to find out the position of the court in your circuit, and let that be your guide. Here in the Second Circuit it would appear that the Court has left it open for settlement services to mark up fees for their own services even if the prices are unreasonable. That does not allow them to mark up for services performed by someone else. However, could it be argued that there is a service charge for connecting the borrower with an abstractor for recording and update? ...Possibly or possibly not. If the U S Supreme Court determines that the rulings in the Second Circuit are wrong and reverses them, there could be some serious financial ramifications for those who relied on these rulings. Financial adjustments may be required. Unreasonable mark ups in service charges could become a huge problem in the future even in the Second Circuit. I think the safer course to follow is to charge for expenses actually incurred with a reasonable charge for services actually performed by the settlement services.

If you are located in a Circuit that follows the opposing rulings of the Fourth, Seventh and Eighth Circuits there may be problem with unreasonable mark ups on prices entirely.
You might consider contacting the state Bar Association for an informal advisory opinion. The Bar Association may even have already dealt with this issue previously, and may already have an opinion on record. The opinons of the state Bar Association are not law. However, they might cite relevant law, and give you a feel for the position of the court on the mark up issue in your area.