#1 I believe is usually $2,000.
You might take a look at Baltimore's Star-K shadchan incentive program. They're now paying $2500, which is supposed to approximately match what the shadchan would receive from the family. In fact, it's conditional on the shadchan receiving at least $1500.
The Star-K program pays the shadchan shortly after the wedding, and thus won't pay if the engagement is broken before the wedding. I don't know if traditionally a shadchan is paid upon engagement or marriage, though it would seem strange to pay someone and then demand it back (barring the shadchan hiding some serious, serious problem about the prospective bride/groom).
There seems to be some norms and standards about paying shadchanim of which I'm unaware, hopefully others will fill it in. For instance the Star K says if Mrs. Goldstein thinks of the shidduch, but then hands the idea to Mrs. Cohen who spends hours and hours on the phone making it happen, Mrs. Goldstein is paid 1/3 and Mrs. Cohen 2/3.