Lkwd mom:
Glad to see we are on the same page!
To answer your question I would think (based on input over the years from many shadchanim) that for the active shadchanim the money would be more appreciated for numerous reasons (the least of which is how many candy platters do they need already :).
If it’s accompined by a nice card, that would add a tremendous touch and give them alot of chizuk.
The exact amount is something only you could know. It would depend if it was a easy shidduch a difficult one, one date/eight dates. Whatever you feel is appropraite is the right amount and whatever you give them they will GREATLY appreciate.