For the least commonly taught languages, there may be only one or two examiners in the association's national network. This may require that the program bring an examiner to your campus from a greater distance than anticipated. If the issue is simply one of distance, a coordinator probably would be well advised to arrange for an examiner's travel, lodging, etc., even though it may cost the program more than had been budgeted. It is hazardous to impose inordinate austerity in this area of the program's budget. Yes, at least once, at the end of each term.
Many programs also bring examiners to their campus for mid-term testing as well, for a briefer exam.