Advice on coloring my hair?

My hair is currently between medium brown to auburn. I want to get it blonde underneath and a chestnut color on top. Here's my question: to cut down on costs, I was thinking of doing the top color myself, and then letting a salon do the blonde underneath. Would this be a good idea? Most salons charge $60-$100 just for color, but for two colors, especially going from my dark color to blonde underneath would be expensive. Any thoughts? And I don't need comments from people saying "oh, you shouldn't do those colors, do these or blah blah blah...I'm only interested in opinions from stylists or someone who has had experience with the same situation before. Thank you.