Answer: HORSETRADER

A horsetrader is someone who engages in the buying and selling of horses, often with the goal of making a profitable deal. In the given clue, "One ponying up for a deal," it suggests that a horsetrader is someone who is willing to pay or offer something (in this case, a pony) in order to make a deal.

Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: One ponying up for a deal?. Explanations are generated by AI and may be inaccurate.