First I need a good beginners bike that is big enough for me.

Second I only make $7 an hour at 23 hours a week, so I need a cheap bike.
Third I CAN NOT get a loan, so I need to pay cash. So again cheap bike.
What big cheap beginners bike would you guys recommend? I am looking for a bike (new or used) for about $3000 after registering and even that is going to take me 6 months to save for.