Dan, there are a set of Ervocoms on there at the moment. They are £380 or offers, but the seller has had 9 offers and not sold yet so I can assume he wants the best part of £350 for them.
Or as Dave says there seems to be good feedback for Refs Call flags, are they are considerably cheaper at £169-200 (depending on the flag design you have).. So it depends what kind of outlay you are looking for really!
Can you justify a set of Ervo's as a first season L4, if yes then grand, but if not then the RC ones are a solid alternative.