The concerns surfaced after a meeting last week at which plans to award a "quality mark" to legitimate contractors were adopted by a government-backed taskforce on cowboy builders.
The plan has been drawn up by a taskforce working party led by Sir Michael Latham. It will require trade associations to set up "certifying bodies" to award quality marks to members.
These would be awarded according to technical and financial criteria, and the award bodies would be tested by the UK Accreditation Service.
Contractors with quality marks would be visited by the certifying body once a year. And, every three years, the financial propriety of their dealings would be investigated.
One industry leader estimated that firms could face a £500 bill from the certifying bodies to obtain the quality mark. Another said: "What rankles is that reputable companies will incur expense to cater for the great unwashed." But Sir Michael said: "I can well understand people's nervousness, but we have undertaken this exercise on the premiss that the government wants a quantum leap in public protection.
"It's not good enough to just say that everything is OK as it stands now. If it was, there would be no need for any expense. But with the situation we have, there needs to be some pain and expense to set up a credible system of inspection.
"The figure of £500 has been floating around, but not with much conviction. Clearly, there will be some start-up costs and money will be needed to cover inspections, but this needs to be done with conviction."
The issue of cost was debated at a last week's meeting of the taskforce, which is headed by Tony Merricks, general manager of Balfour Beatty's specialist contracting business. Several other working parties are to contribute to an interim report from Merricks, which is due to go to construction minister Nick Raynsford in February.
One is studying how warranties can be used to crack down on cowboys. There has been some debate about how well these can work in compensating clients that have been the victim of cowboys.
The main argument is over the price threshold for the warranties. Contractors believe firms should restrict them to work worth more than £500. However, local government representatives on the taskforce want this reduced to £100, as cowboy fraud is particularly prevalent in the £100-400 price bracket.