Painting - Cost estimate to repaint over dark colors

I'm looking to buy a particular house. The current owner apparently likes dark colors-blue green, etc.. The house is great but I would have to repaint it all with more neutral colors(ie off white). It's approximately 3500 square feet with 9 foot ceilings. I heard you have to paint dark colors twice if you're going to white. Anyone know what this would cost? I need to get some estimate before I make any offers.
Thanks

Figure one coat of top quality primer sealer, and one maybe two coats of top quality paint. You might do it with one of each, but your budget would feel better figuring two coats of paint.

Don't forget to think about giving the ceilings a nice fresh coat, while you are at it.

HTH

The way I used to figure paint jobs for walls and ceilings was
.25 cents per s.f per coat if I was buying the paint and .20 cents per s.f per coat if customer was buying paint. now when I say s.f. I mean of wall space. Measure the width and height of wall and multiply these #'s that gives you s.f. of that wall, now do the same for other walls and ceilings then add all together and multiply x .25 / coat. Trim and base are extra if different color. Hope this helps :)