Cost of Project Controls- is there an industry standard?

I can not answer you as far as the research, but from experience, Yes that % seems reasonable. Now I am going to write from a General Construction Contractor Standpoint. When you make a budget for a project, the project management cost (which includes the people who will do project controls) is included part of the general conditions (or general costs whatever you call it). And this general conditions is usually anywhere from 5-15%. Deduct things like your jobsite trailer, office equipment, fire watch, safety etc... you are left with 5% at the most for the whole project controls + site supervision. Deduct site supervision and you are left with around 2-5% just for project controls. from the jobs I worked on I can tell you that this would be the average.

In order to be a little more scientific, you can use the total number of project management hours needed per a certain scope or dollar value of a job by using your historical data from previous jobs. Another approach would be to take your schedule, multiply the duration by the cost of the PM staff that you know you will need for that size of job (of course dont forget that at the beginning and end of the job you will need less PM staff). One thing I just remembered was a curve presented in the PMP book that showed staffing needs on a project where it peaked in the middle. You may want to check PMI standards to see if you can see something.