I want to start skateboarding again any tips?

I used to skate like 2 years ago and I want to start again. I used to only be able to do an ollie and almost a kickflip. Now i am determined to do more tricks. I am also doing it to lose weight for exercise along with other things. I have an old board but the trucks are rusted and what not. I want to buy a new board but don't want to spend more then 100 on it any help?