Actually quite simple,, sort of. Race far simpler cars with basic safety rules. Ban exotic materials, ban a lot of the electronics. No forced aspiration and less emphasis on longevity of parts, Though there is still a case for some of that. That and petrol engines of X capacity [3.5 litre?] With say 12000 rpm max. No more than 6 speeds, no drivers aids which can be controlled with control ECUs. mechanical suspensions. And no stupid boring hybrids!! They cost tens of millions and make the racing less.
More emphasis on the drivers and less on electric gizmos,, and cars with simple aero, not the mad boffins nightmare we currently have. Wings with no more than 2 elements either end. flat bottoms and mininum ride heights. No control tyres, maximum rim widths and diameters and mininum duro on the tyres. Read moderatly hard, like the hard tyres are now.No super softs that last 5 laps and just turn the track to marbles.
That should make simpler, more entertaining racing, and a smaller budget team that is half smart may well find themselves on podiums. Even if they do not it has not cost them the National debt of a small country to do so!