Forced to interrupt their world tour back in May so that frontman Bono could undergo back surgery in a Munich hospital, the cost of postponing a U2 tour is massive – reportedly, AUS$18.9 million, in fact.

The Irish rock legends were forced to take time out from their global U2 360° trek a few months ago, cancelling their headline position at England’s Glastonbury festival in the process. According to insurance brokers Robertson Taylor, despite being ready to go back on the road now, the delay to their North American shows and the festival has set them back millions – not good for a tour reported to the most expensive (and the most profitable) in the world.

U2 are set to resume their tour on Friday 6 August in Turin, Italy, and will return to the US in May 2011 to play their postponed dates. While no Australian dates have yet to be announced (a December visit was rumoured), Mark Fisher, the band’s stage designer, let it slip to an Aussie newspaper that the band will end one of their tour stints in 2011 in Australia, so they can take a break afterwards.

The “Elevation” outfit are also currently reworking at least two of their old songs with producer Dave Hollister, who used to be in a R&B outfit called BLACKstreet. Hollister revealed via Twitter that he was collaborating with Bono and co on the tracks “Grace” (from 2001’s All That You Can’t Leave Behind) and “All I Want Is You” from 1988’s Rattle and Hum.