I would suggest giving $1 Billion each to GM, Ford, Chrysler, Honda, Toyota -- and and all established car companies with production in the USA; and give $1 Billion each to Aptera, Tesla, (maybe ZAP! if they can show they are legit) and any other start up that has existed for say 4-5 years. We should not play favorites, or pick winners.
This totals ~$8 Billion; leaving 17 Billion.
Pay $7 Billion to the first car company to start production (and produce 10,000 units) of a car that seats four-five that gets at least 50mpg on the combined EPA test. (The Prius already gets 40+ on the combined...)
Pay the remaining $10 Billion to the first car company that starts production (and produce 10,000 units) on a 2+ seat car/vehicle that gets at least 75mpg on the EPA highway test. This car/vehicle would have to be a plug-in hybrid, or be a biodiesel, or be a pure electric with a range of 100+ miles.