hello, is this 50 GB for me for three months? costing 120$?
The way it works is you're not obliged to use the full 50GB in 3 months. At the end of 3 months, whatever amount of data you have left over from the 50GB will carry over provides you renew your 3 month or one year membership.
Data never expires as long as you have an active membership.
To get an idea of the monthly cost. Use this calculator: