I have just gone back to brown from bleached blonde, I know how you feel about the regular maintenance and cost of roots! I went to a salon as it is tricky, but they coated it RED first. (bright orange really) and dried it completely before putting the brown on. The colourist explained that although this looked shocking (for all of 15 mins until dried and dyed) it was VERY IMPORTANT to have a red base to 'warm' the brown colour and stop any khaki shades bleeding through. It's worked wonderfully and perfectly matches my roots. There has been slight fade where the bleach is bleeding through but it just looks like lighter brown highlights, nothing drastic. (it's been nearly 3 months). I recommend if you can, go to a salon and just grin and bear the cost one LAST time as bleached hair reacts so differently to 'normal' hair. If that's not possible, put a red base on it first and dry before dying.
Good luck!