I don't smoke or use drugs, rarely drink, and have only stayed in a motel one night so far (if you count the Doyle as a hostel, as I do). I have not pink-blazed at all yet, either. Over half my hiking food is mailed to me via maildrops. My largest gear purchases after I have started my hike have not been out of the funds I carried with me (new pack when Dana proved to be a lousy pack when used for actual hiking, 3 pairs of trail runners, some of my maps, some of my Aqua Mira, etc.) I eat considerably fewer restaurant meals than do most other thrus I have observed, often just getting 5 bucks or so worth of cheap canned goods (per day in town) from the local dollar store to eat while in a Trail town. I have already run through over $2K. I would say that anyone who budgets less than five grand for a thruhike is planning very unwisely, that their odds of completion are thereby considerably lowered. Too, their hike's enjoyment level will be much reduced as well.
My advice? Raise your income and/or lower your expenses enough to have at minimum 3x as much money saved as you are planning.