Gran Turismo 4: Easy Money Tips

Hello everyone, welcome to my guide for earning easy money in Gran Turismo 4. This video will tell you 5 easy and quick ways to earn money in GT4. For the people like me still interested in playing this wonderful racing game. Like Gran Turismo 4, it is surprisingly easy to earn money in GT4 once you learn about a good portion or the races and features in the game. Which is a good thing since some cars can be quite expensive, mainly all of the race cars.

I hope you guys enjoy! :D

As usual to my videos, the song list is here! They're all basically songs from Gran Turismo 4's menu tracks and I think they're all composed by Isamu Ohira. Anyway, the name list:
1. Replay Theater Theme
2. Drift of Air (GT4 Mix)
3. Be at Home (Remix of Soul of Garage from GT1 & 2)
4. Hypnosis
5. Pre-Race Menu Theme
6. Light Velocity (GT4 Mix)

Alright, this is the Q&A section. Just in case you're still confused on a few things.
1. "Can you win the same car again?"
A: Yes, the video would be different if you couldn't. Winning the same car multiple times is the key to grinding in these early GT games. So, if you sold the Mercedes-Benz CLK LM for instance, you can win it again.

2. "How do you win the same car again.?"
A: This depends on which event type you're doing. If it's a single race event like Capri Rally, you have the clear the wins away when the game asks you. Then, you just re-do the event to win the same car.
For championship races, you just have to enter the championship again (hit the championship icon) and re-do the event.

3. "How do I clear the races?"
You just have to click on one race you beaten and it will give you the option to clear the event. Just choose clear and the races will reset. Now you're free to win the same prize car again.
Note: Do NOT do this on championship races. Just re-enter the championship option again and don't bother with picking any track.

Alternate Methods suggested by commenters:
Jamie Facco JJF suggests entering the Opel Speedster Trophy event to win the Opel Calibra DTM that's worth 375,000 cr.
Side-Note: It was suggested as a joke, but I actually think that's not too bad of an early credit farming. I mean, if you can modify the Speedster; you probably can use B-Spec to win this with ease. Though, I haven't tried it yet.
Whisky mentions doing the El Capitan 200 miles Endurance with the Pescarolo C60 Judd Race Car on Sports Hard Tires. Use B-Spec mode to speed up the race and it should take around 45 minutes according to the user.
Note: Endurance events aren't really my thing, which is why I probably didn't think of this. I avoid them like the plague if I'm honest.
chipsnever957 said that the Laguna Seca 200 miles endurance was a good farming spot as it'll win you 250,000cr in prize money plus the Ford GT40 worth 750k. So, about 1 million cr within 45-60 minutes of racing on B-Spec mode (via x3 Speed up).
Similar to above, I don't like endurance events, but maybe others are less bothered by them.
IIGrayfoxII suggests completing the Mission Hall to unlock the Nissan R89C and win the 24 hours of LeMans Endurance event.
Note from me: Requires a lot of patience and leaving your PS2 on for multiple hours. Would recommend making sure you have time to do this. Also, have a lot of patience for the driving missions. They're going to be tough.
Like other suggestions, I probably won't do this myself as I never liked doing endurance events. However, I say for people that enjoy them; have at it!
*Kirlan Lion reminded me about the "La Festa Italiano" event and it's prize car being the Alfa Romeo 155 DTM. It's worth 265,000 credits and the event itself could pontentially be finished in 7 minutes when using B-Spec mode.
Okay, I just plain forgot about this. Great idea!
*Buster Johnson mentioned using a fully-modded BMW M3 GTR and winning the the final championship with it. The prize car being worth almost 400k. I think he's talking about Schwarzwald Liga B and the prize car being the Mercedes-Benz 190E DTM.
Note; I can confirm from experience that it's worth close to 400k cr. Though you don't have to use the e46 M3 GTR to win this, I recall doing this event with other cars aswell. Just grab a German car that can dominate the race with ease and you'll be fine.

Timestamps:
0:00 Intro
0:24 Capri Rally Easy
4:46 Tsukuba Circuit Wet (Normal)
7:20 Stars and Stripes
9:45 Japan Championship
12:36 DTM Championship
15:57 End Section