How about a function room? Some condos (else can try renting from your nearest CC) do have a bigger function room that can surely accommodate 100 pax. Also, function rooms are definitely cheaper than if you were to rent a venue outside. Can also consider 7th Heaven (ask them for price) or book a chalet (probably have to split into 2 sessions).
How about engaging event management agents? Or at your kid’s school or rent a cafe for the 2-3 hr duration.