Teaser deals in adverts are masking the long-term cost of broadband packages, a charity has claimed.
Citizens Advice said that hidden charges such as line rental and delivery costs could add £20 a month to the advertised price.
It highlighted one case in which a customer would pay £465 more than the amount advertised during a contract.
The trade body for internet service providers, ISPA, said broadband prices were "clearly presented".
Nicholas Lansman, ISPA secretary-general, said: "It is important that customers look at the full terms of an offer when choosing a provider.
"Ofcom recently concluded that the UK has one of the most competitive broadband markets among major European economies, as the average price of a fixed broadband package has fallen by 40% and speeds have greatly increased."
'Up your game'
Gillian Guy, chief executive of Citizens Advice, said confusing teaser rates and hidden costs made it difficult for consumers to work out whether they were getting a good deal.
"Internet providers need to be upfront about broadband costs, ensuring adverts are transparent and people know what they are signing up to," she said.
"Some broadband firms are starting to accept that prices need to be clearer. Now the whole industry needs to up its game."
The charity said that line rental was the most expensive additional cost.
The ISPA said that service providers using the BT network were required to levy a line rental charge, which went toward maintaining the network used by most of the UK for both phone calls and broadband.
The report comes as Virgin Media was criticised by the Advertising Standards Authority (ASA) for one of its broadband adverts.
Two customers complained that they had signed up to the operator's 12-month broadband contracts only to be told that their monthly charges would be increasing during the minimum term. They said this was misleading.
The company argued that it could not predict price rises at the start of a contract and so was unable to advertise potential increases.