There's a formula that's used based on things like how many years a player was in our development squad, first team appaearances etc.
It also depends on things like which league the team that signs him is playing in.
Because Cadden has come up through the ranks, that counts in our favour.
It was the same formula that was used when Lee Erwin moved and landed us about 400k (from memory). It applies up until the player is 23 years old.
It's also what makes it near impossible to sign any youngsters from the lower leagues in Scotland as it puts them well outside the transfer fee range we are prepared to pay.
I don't have time right now to dig out all the details, but I found this piece that discusses the formula used in England (I think it's different for cross border, but gives a decent idea) It's also a little out of date:
That calculation was referenced in a discussion about kids moving from club to club when they were 13 or 14 years old.