SAE +stamp or IRC

[jhan]

Hello, I want to send a request for an autographed photo to UK.
Is it better to send SAE or will they be using their own envelope to reply? I don't have a photo I can send, so I don't know the size of the photo they may send back to me. So I was thinking of just not sending SAE. I know people who got their autographed photo in the agency's envelope.

also, how many, on average, IRC's or stamps are needed for a regular autographed photo? Like how many did you guys send?

ahh this is my first time sending a fanmail requesting autograph and DO NOT want to waste money sending it or not get autograph back....

THANKS!