I was wondering if some of you out there are arrangers, or at least have done some arranging and gotten paid for it

I am beginning to get some arranging jobs and need some general advice about what fees to charge. Are there any general standards? And if so, should I be charging by the job, by the hour, by the number of instruments and measures, or some other criterion? So far, the requests are for a small orchestral ensemble--about 25 players. But I should be able to extrapolate to cover smaller or larger groups. I very much appreciate any advice you may have. Thanks, Plutarch