Hiring a wedding band can easily cost thousands of pounds as the fee needs to cover the band's transportation, parking, liability insurance and engineers for the sound and lighting.

Geoff Walker, leader of the UK-based Ambassador Band said his fee for a 16-piece wedding band with lights would be around £16,000 ($21,500).

Banana Split's Jamie Simon says hiring celebrity performers would put the costs through the roof and possibly add millions of pounds to the bill.

Then again, some performers might be so keen to perform for the royals that "maybe they'd do it for next to nothing," said Niemierko.