So I'm unsure if I mentioned this previously, but I had this neat approach to trying various cars in events while tuning them as little as possible. Y'see, more recently, when buying a car, I'll just get a ballast, power limiter, and similar sets of tires, and not even a full-customize computer. No widebody in GT Auto, either - if anything, a removal of the front license plate. This not only saves credits otherwise used for tuning, but also lets you drive a car closer to its stock condition, even if it means potentially changing the power/weight to comply with various regulations.
Let's take the Race of Turbo Sports Cars for example. The regulations state that your car can have no more than 700 PP, plus it needs to be turbocharged. You could get the Bugatti Chiron and slightly adjust its power/weight, since it's got 705 PP as-stock on Sports Hards, or for about a tenth of the price, you could get a Ferrari F8 Tributo, which comes on Sports Mediums and thus has 693 PP. What I'd do is get the F8, then buy some Sport Softs, which upon installing should get it above 700 PP. Then I'll likely tinker with the ballast and power limiter until it's even closer to 700 PP.
At any rate, I encourage you to list a regulation that's somewhere within either World Circuits or the Missions, and then I'll see what I can recommend. Even if the PP for an event is only a suggestion, I still think it's fun to try getting the settings just below it.