An anecdote: a good friend of mine just found out she's pregnant with her first child. She's a huge Harry Potter fan, and her favorite characters are the Weasley Twins.
For not-all-that-much money, I was able to get James and Oliver Phelps (the actors who played the twins in all 8 movies) to each record a separate video message (about 1 minute each) wishing her congratulations by name and wishing her and her baby well.
I made the two Cameo requests on a Friday night, and had both videos by Sunday morning. Both were warm, friendly, and seemed to be genuine and happy for her (obviously to the extent that they know her: "name is X, first-time mom, huge fan".
She was absolutely over-the-moon happy about receiving them.