This should not be difficult if you start on a middle team and work your way up to the top teams beating all objectives and finishing on podiums and winning. Again if you are struggling try setting the AI to "Amatuer" so it can be easy to finish on 1st.
You will get more point on Medium than Easy and more even on Hard. (Hard does not mean hard AI, simply that you start on one of the worst teams), so it might be worth a shoot at Hard if you are close to 25k. I got close to 40k winning all in Hard so there is a lot of room even if you can´t win all races.