Worth = what the two parties to a transaction deem acceptable. Sitting on the outside, frankly, it's bizarre to discuss this.
Some people here think Lukaku is "worth" more...and others feel Ronaldo isn't worth more than 30 Mn (I kid you not; this was on the Ronaldo thread).
It's all relative and I don't think professionals like Woodward are in the business of getting bent over and shafted if there are alternatives available.
In the end, if the managers and the club bosses of both sides accept that a fee is "acceptable", that's the worth. Simple as.
PS: Some people don't think it's worth it to spunk money on a Lamborghini, while others would do it without a though. Similarly, I don't think poisoning myself with colas is "worth" even getting paid for, but people actually pay to do it. Who's to argue what's correct? Same principle applies here. It's only worth what the parties to the transaction think it is.