I found an interesting post on the website dangerousminds.net that reproduced an article from the December, 1966 issue of Rave magazine, a English popzine from the 1960's. George Tremlett, an English pop journalist and author used London Board of Trade information to estimate the wealth of the four Beatles. Around 1966, Tremlett estimated Paul's wealth at 1,195,000 British pounds or--3,334,050 U.S. dollars. That's 3 million. Tremlett mentioned the confiscatory British tax rate but also said that Paul might have income unreported to the Board of Trade. (See magazine chart below.)
There has been alot of speculation that our Paul just up and walked away from The Beatles. He could have exited gracefully, if he had wanted to, and retired--publically--a very wealthy young man. Instead, he disappeared and was replaced, and that's why Paul researchers are tracking down what happened to him.