There is no Dodge Intrepid in GT1. The only way to get the Dodge Concept Car is to get all golds in your B-license. (And that car is not FF anyway).
Unlike GT4, in GT1 FF cars handle unrealistically well. That is, they can take heavy power mods, and get the power to the road.
In North American versions, the Mazda Demio A-spec you win from the Sunday Cup is perfectly adequate, especially if maxed out. Especially since you say you don't want to waste any money, that's probably the car to use. But you are using the PAL version, so it won't be the fantastic star it is in the North American version. But I'd guess it can win the FF series. By special arrangement, it's also eligible for the Lightweight Battle Stage.
Based on Arcade Mode, you'd likely favour the Mitsubishi Eclipse. Any of the FTO (new, or used, not the weird 4WD FTO LM prize) are overpowering choices too. And the Honda Civic 3dr'93 si is far and away one of the best cars in the game, in proportion to its non-excessive but reasonable max-power, anyway.