You want a room that feels special, where the guest of honor can actually hear the toasts. Private dining rooms in the US usually run about $1800. Booking a Tuesday or Wednesday night is the move here. Most restaurants drop their minimums on weeknights, which gets you the same food and service for a lot less.
High-end spots fill up months in advance, so lock in the venue at least eight weeks out. Once the room is set, you can figure out the menu and the guest list. We use the lead time to break that cost into manageable chunks instead of one giant hit to your bank account.
The catch is that this 18-month window is a deadline, not a gift. If you still have a balance when the period ends, the standard interest rate kicks in and the debt gets expensive fast. Pay it off on time to make the math work in your favor.