2000' max for a flare. Even a two stage Estes rocket with three stages using D size engines will only go about 4,000'.
Whoops, make that a three stage Estes with 3 D Engines will only go 4,000 feet. You can add that the conditions have to be perfect. Virtually windless.
But a totally illegal, tweaked Estes (with Soviet style multiple parallel motors) might be able to eke out something over 5K ...