That are still 16 skin -> one simple professional looking skin takes about 10 hours (or more) -> 160 hours for all the cars you want * 10€ per hour = 1600€ I don't know what you want with a single skin. I doubt that you could make the other cars.
You should visite Master Skinnerz there you'll get a lot help making your first skin and you can download the great skin kits Bunta made.
You really should try to make it yourself it's not that hard. If you learn how to use the path tool in photoshop you should be able to make a G4 RTR skin for lfs.