$70 might be a lot for a basic cover charge, but by North American standards, $70 isn't that much to pay for admission to major club nights or circuit parties. $70 is pretty much middle of the range for such things, and major events commonly run up to $100 or more. Compared to that yardstick, the megaclubs in Ibiza aren't out of line. Of course, at such events in the US, the crowd is very heavily gay, so you don't have to deal with the drunks starting fights and you can be fairly confident that checking someone out won't get you a punch in the face.
It's interesting to see the comments in this thread about the scene in Ibiza. I've been curious about it but never felt the uncontrollable urge to go. I suppose my thinking is that if I'm going to take the trouble to go to Spain, I really want to see the country, not spend all night inside a club. For Europeans, I'm sure the perspective is different since you've likely already been to the Spanish mainland and it's so much easier to get there.