Free to play (F2P) games are all the rage, but the F2P MMO, RIFT is unusual in that it's basically still a subscription game masquerading as a F2P game. So... how much does it cost? About the same as WoW is the short answer.
The long answer is that you pay nothing to get started, but access to much of the new content for higher levels requires some degree of purchase. Fortunately (and craftily) there's the equivalent of a boxed set that gets you all of the important bits up to, but not including the most recent expansion: RIFT Essentials Edition. For $50, this gets you everything that you really can't play on the same level without (additional skill trees, an extra calling (class) and two additional gear slots among other goodies). Once you have that, you should probably play the game for a while and see how you feel. Becoming a subscribing "patron" gets you some nifties, but nothing that's essential. Then there's the most recent expansion ($40) which usually buys you the extra features, levels and content of the expansion.
So, for the complete functionality of the game, once the new expansion, Starfall Prophesy comes out, you would pay a total of $90. The ongoing patron subscription really doesn't add much to that, but if you wanted to do that, it would be an additional $11/mo. if you buy the annual version.
It's cheap entertainment at that price (especially when compared to going out to movies or dinner) but it's certainly not the free game that they might tease in their ads.