This is correct. It is actually a 3000 CSC amount but when you buy $30.00 worth of CSC at the same time, you automatically get a 500 CSC bonus.

3,500 Cash Shop Credits Price: $30.00 500 CSC bonus!

The extra 500 (or 1000 in this case) is a bonus so the event only shows the original amount.

I'll ask if that can be made more clear but I think they don't want people freaking out thinking that they paid $35 when 3500 CSC comes up xD