No, it's not about money. The BRDC had the money to upgrade Silverstone's pits all along. They decided that they didn't want to spend it because at the time, they didn't think they needed to upgrade the pits. The money itself had not been taken from some other project, and then re-committed when the BRDC decided they didn't need to upgrade the pits. It was just sitting there, doing nothing except maybe earning interest. If anything, it was in their interests to spend it. The pits were, quite literally, falling apart. Like I said, teams had to bring their own floors just to complete a Grand Prix weekend simply because the existing floors were in no condition to be used as they were.
The problem here was the BRDC caring more about the history of the British Grand Prix than the future of it. They had the motive, the means and the opportunity to turn Silverstone into a world-class facility, and they still chose not to, for reasons that are probably known only to them. They pride themselves on being one of the best racing circuits in the world, and yet they didn't want to spend the money (which, again, was doing nothing) to actually make the circuit live up to that claim. In the end, Bernie had to take the race away from them just to convince them that they needed to upgrade the pits - something that they had been both planning and able to do for at least five years before they actually lost the race. Money has nothing to do with it. Idiocy was the BRDC's problem.
Now Bernie wants Montreal to upgrade their pits before he renews their contract, because the current ones are 25 years old. They desperately need it, too. Just watch how quickly the organisers agree to it, because they know their pits need work.