I don't know cost of all items, but you can save mostly on windows:
10 psc of white windows cost total 3-4 USD
10 pcs of tan windows cost total 12-20USD
Small windows are more important because you need only 4pcs per car and they are not very expensive, but you can still save money:
4 pcs of white small windows cost total about 0,6USD
4 pcs of tan small windows cost total about 2,6USD
Personally I prefer white-green cars more then tan-brown :-)