What's the easiest & quickest way to learn to speak Farsi?

my dad is full Iranian & my mum is English, but they divorced when I was quite young & I don't see him often so I never got the chance to pick it up properly :( I've learnt a few phrases here & there but I want to be able to have a full conversation with my family & friends! I don't have alot of money to spend on things like Rosetta stone, any suggestions? X