As all my huge expenses (proposal, banquet, honeymoon, renovation, etc) are coming soon, how much should the groom be expecting to spend on the betrothal ceremony?

My advice is to speak to the bride parents aka your future inlaws.

The betrothal ceremony is just... a ceremony.

But the significance of it depends on how the elders look at it. So be tactful. May not be that important to the couple, and with the modern mindset, some parents look pass it too. So try to spend as little as possible - as some items may not be used. Wedding dinner should still be the bulk of cost.

Similarly the jewelry to some is just for 'face'. Gone are the days when you will "pawn" your gold for money.