Extra pilot start-up costs were my first thought, but when you think about it, the episode doesn't have much out of the ordinary budget-wise. You have two actors intended to be regulars (Lansing and Garr) and an unimpressive office set with some futuristic devices in it (partially cannibalized from an earlier episode).
That doesn't reasonably add up to $288,049.00 (the budget in question).
In comparison, "The City on the Edge of Forever" cost $250,396.71. The first plot cost $615781.56, and the second pilot cost $354,974.00.
For AE, casting had to rent a cat that could change into a human female. That can't be cheap.