I assume, you are playing on the international
pokerstars site. In that case I will recommend you to focus on the 1$ 45 man SnG. Its a little bit aggressive with a 70$ bankroll, but since its a 45 man, its still kind of fine to play with 70 bullets in the gun, whereas for a 180 man that would be to aggressive. And should it go south, you can always move down to the 50c or 25c. Or pop a bit more into the account. Its not like, losing say 30 or 50$ is a life changing problem for most people, and if it is, maybe you should not spend time playing poker.
The reason, why I prefer the 1$ 45 man, is because the 50c versions are all turbos. And in my experience the turbo SnGs on PokerStars are more difficult to beat, because they are simply to fast. Its difficult to find a lot of edge, when you are reduced to push-fold poker after just a few orbits. The regular speed 45 mans (there is also a 3,5$ version) gives a more reasonable mix of push-fold poker and postflop play, where you learn more, and where skill edges have a better chance to show.