I"d recommend just buy it, I'll do some quick math for you.
On Amazon you can purchase the digital download for 19.99, I"m not sure if it comes with a free trial but even then that's just a 9.99 fee. Since you are doing this before May 31st you'll be eligible for Legacy as long as you pay for 90 days cumulative aka 30 dollar investment. By doing this your game sub will only cost 9.99 for as long as you play and you'll be entitled to having 8 chars on each server when 2.0 comes around. If you don't do this then you'll have to pay the following
12.99 for one char on each server=$156
14.99 for 8 char on each server=180
Legacy 9.99 for 8 on each server=120.
So basically is you take these values at face value then I"d say risking the $30 dollars to try the game is worth it, then it's 140 in a sense for legacy for that year but then after that you'll only be paying 120 a year compared to 156/180 which saves you 36/60 and even then by just buying it now and becoming eligible for legacy you save your 16 dollars.
Then again if it turns out to be a bust for you then you only lose out on 30 dollars so I really don't think it's to bad of an investment to make considering that by buying it now you at least open yourself to the opportunity to obtain legacy. http://lodestone.finalfantasyxiv.com/pl/campaign/campaign.html#legacy