You could say that in modern terms the 3 of them cost £190 million as it was slightly over the cost of the world record transfer.
one way to look at it was that the transfer record involving a British club at the time we signed them was £115,000. It's now reckoned to be £105,000,000 (Coutinho). Applying the same ratio now as then we'd be paying about £36.5M each for Waggy, Houghton and Butler. This does show both the ambition we had in the mid-60s and the ever growing gap between the richest clubs and the rest.