I suggest you mine. If you do decide to mine, do it around the y:9-12 coords, but if you don't mine. You can always farm melons and wheat and what not.
I agree with ct that mining is how I earn money the fastest when needed. As for farming, I would recommend pumpkins instead of melons though unless you have a melon sword (about 500k)
Yea true about the pumps and when you mine try to atleast an eff 4,unbreaking 3 diamond pick if you can, it'll help alot!
Yea, think about it... If you only played an hour a day and dedicated your entire time to pumpkins, it would take you about 10.5 days to get 85k. However I suggest you should aim for 100k before applying, that way you still have a little bit of money to get you going.
It's not meant to be easy, they call it a "Hardcore" economy. One piece of advice, stay away from renting star tools. If you rent per hour you're not making much more money (if you break even compared to the regular rate), and if you lose it you're in a lot of trouble.