Ok, I've made my mind up.
I've asked a few users and i've gotten a range of results.
I've made a mean average out of it too.
Dbuffed, Zerker, Decode, Jonny, Sysm participated.
The amount you will need to refund @Adapt is 153.6M OSRS
Since it is indeed a big sum, you'll be given a maximum of 4 days from now to refund @gh0st unless gh0st does not mind in giving you extra time.