Forget, got another offer...

Able to pay? Your team must have a good sponsor if you are willing to pay more then 1000€ for a skin pack (20 cars + 12 unique helemts) that should be about 20*8-10 hours = 160-200 hours for the cars and 12*10-15 hours = 120-180 hours for the helmets (you want unique so new design for each helmet)

You want good quality that's why i count with >10 per skin. A good skinner probably won't work for under 10€ per hour.
So you would pay at least 160+120 = 280 * 10€ = 2800€

Your team really should try to make the skin, you won't find a skinner that makes a skin pack + 12 helmets for free.

Making a new skin fun making 20 times the same skin for different cars is pain.

WOW thats one hell of a request. You could do with a team of skinners not just a one man band! 32 skins........

Have you tried asking at master skinnerz, i'm sure you'll find one or 2 guys interested there, plus you've got the added bonus of being able to have a look at their labs/garages/... (portfolio)