I would say probably around 1-3 hours to complete, and if you want to purchase the game on it's own it is currently any purchase of $4.49 or more.
how long is the other game on its own and how much just for it.
Slave RPG is $8.99 on it's own right now, and the length really depends on how much time you want to put in it. I would say around 3-5 hours for just the base game, but you could easily put 10+ hours into it.