In Evenepoel's case, the number Lefevere gave was simply to say, it's not gonna happen. He could also have said 1 billion. The thing is that they got QuickStep to raise their budget, and get Soudal onboard to sponsor a lot more than they did at Lotto, and both those sponsors did so under the condition that Evenepoel was on the team. That means legal issues would be a lot more complicated and probably Evenepoel would have signed additional contracts.
In any other case, in Belgium at least to my knowledge, any employee can get out of their contract if they pay the equivalent sum equal to what the contract is worth, which is the number the employee would get paid over the remaining duration of the contract. So if Vine would have 2 years on his contract left, and gets paid 100.000 euro per year, he would have to pay 200.000 to get out of his contract. Which UAE would obviously be happy to front him.