Calls for the U.K. to abolish the monarchy and become a republic are ever-present, but they tend to tick up during big, royal-centric events. Still, about 80 percent of Britons approve of the monarchy fairly consistently.

And that may be for good reason -- there's at least some evidence that the monarchy brings in heaps of tourism revenue.

According to Buckingham Palace, sustaining the royal family costs Britons 53 pence, or about 81 cents, per person, per year. The total came to about 33.3 million pounds (about $51.1 million) for 2012-2013, according to the Palace, up from 32.4 million pounds the previous year.

However, the awesomely titled Sir Alan Reid, Keeper of the Privy Purse, noted that figure is actually down by 24 percent from 2008-2009, for what it's worth.

But some British republicans -- those who want to abolish the monarchy -- say the actual cost is much higher, once you factor in things like security detail and the cost of preparing for royal visits. Their figure is about 200 million pounds, or $307 million.

The group Republic broke it down to include things like 3.9 million pounds for travel, half a million pounds for Prince Charles and Camilla Parker-Bowles, and some 400,000 pounds for public relations.

The royal couple's bundle of joy will drive up that cost, of course, as babies tend to do. The price of delivery at the duchess's birthing suite in St. Mary's hospital reportedly costs 10,000 pounds, or about $15,300. "Of course, that doesn't include the reported pre-delivery yoga classes at Kensington Palace or visits to private birthing coaches," the Christian Science Monitor noted.

But there's an upside to shelling out for a tradition that some think should have gone the way of the penny-farthing or the Puffing Billy.

The British tourism agency has reported that the royal family generates close to 500 million pounds, or about $767 million, every year in tourism revenue, drawing visitors to historic royal sites like the Tower of London, Windsor Castle, and Buckingham Palace. The country's tourism agency says that of the 30 million foreign visitors who came to Britain in 2010, 5.8 million visited a castle .

Tourism is the third-biggest industry in the U.K., the tourism board claims, and supports about 2.6 million jobs -- or about one in 12.

Baby Cambridge is set to boost consumer spending even more, according to Britain's Center for Retail Research, to the tune of $383 million. (Commemorative tea cups or iPhone covers, anyone?) The chief U.K. economist at the consulting firm IHS Global Insight also predicts that the birth would have an "overwhelmingly positive" economic impact.

What's more, a British firm called Brand Finance, which evaluates "intangible assets," said the royal wedding alone boosted London's economy by 107 million pounds ($165 million) through "accommodation, travel, and nightlife," even while factoring in the economic drag of time off work.