It's $50 a year. So $50 for free game on plus, and $50 to stream PS3 titles on PSV and PS4 (and other limited devices).
I think plus is better. This will work very well for those who want only a PS4 connected, want PS3 games on the go on Vita, and (just like free games on +) would rather rent/stream games for about $9 a month instead of buying retail.
e=mc^2
Gaming on: PS4 Pro, Switch, SNES Mini, Wii U, PC (i5-7400, GTX 1060)