The Country Land and Business Association (CLA) arrived at the figure after a string of events, including the CLA Game Fair at Belvoir Castle in Leicestershire, were cancelled because of the bad weather.
The association predicted the loss of revenue on site and to the local economy for cancelled events, such as the Badminton Horse Trials, to be around £155million, with the CLA Game Fair accounting for two thirds at some £116million.
Around £82million was expected to be spent on site during the three days of the CLA Game Fair this weekend, with £34million due to be spent in the local economy by 140,000 visitors.
Based on calculations from the figures reported when an event is cancelled, the CLA estimated around £30million was lost in the cancellation of Badminton.
A further £4.5m was lost due to the cancellation of the Great Yorkshire Show on the first day and £5million was lost after the Suffolk Show cancelled on the second day.
The CLA said the total cost to the rural economy could be more than £240million if smaller events were also taken into account.
These included the Festival of British Eventing at Gatcombe Park in Gloucestershire, the North Yorkshire County Show, point-to-points and other local agricultural events.
CLA President Harry Cotterell said: "Not only is it heart-breaking when decisions are taken to cancel an event, the direct and indirect economic impacts can be devastating for all concerned.
"This quick analysis clearly shows that at least £150million have been lost to the rural economy, affecting those who organise the events, those who exhibit and trade, and those who attend for a great day out."
Mr Cotterell added: "For local economies, the knock-on effects could lead to small family firms going out of business at a time when trading conditions are fragile and the UK economy is in a double-dip recession."