Seems rather excessive, but it is in ERSA, so it should not have come as a surprise.
What surprises me more is that you pay landing fees the rest of the year as ERSA mentions nothing about those.
You can't hang out and advert for people to come to your airport (i.e.: ERSA) and when they land, suddenly charge them a fee.
No mention of fees in ERSA or in my PPR phone call = no fee for you.