Cost is approximately $15 USD per month for a basic subscription. $30 USD for a Station Pass which allows you to play all the SOE MMO games.
As for level 80.. unless you play on an Exchange server where RMT are permitted, there is no cost to level to 80. However, as always, I recommend taking your time and enjoying the content on your way to "End Game". Otherwise, if you rush, you will be under equipped and under experienced and find yourself in a position where no groups/raids want you.