More than 80,000 vehicles use the two crossings each day, with the cost ranging from £6.40 for cars to £19.20 for lorries.
The money is collected by a private company and the funds are used to pay the construction costs of the bridges.
That debt is due to be cleared by 2018, when they revert to public ownership.
With a general election next year, there is increasing pressure on the political parties to make their positions clear.
Jessica Morden, the Labour MP for Newport East, told BBC's Sunday Politics Wales programme: "I would like to see the tolls reduced and there to be some kind of flexibility in the system, and to make them much more modern so that we could have concessions for people who live locally, [and] off-peak travel for businesses.
"I hope the VAT will come off the bridge tolls so we can reduce them in that way."
Nick Ramsay, Conservative AM for Monmouth, said he would like to see some reduction of the tolls, at the very least.
"I think we could come to a balance whereby you would have a flat rate for the tolls, you would have a reduction in the tolls... and then the remainder that's left could be used on either maintenance or infrastructure," he said.
Plaid Cymru is calling for the tolls to be cut to £2 for cars, while the Liberal Democrats want to see the tolls "substantially reduced".
Alan Williams, commercial manager of Monmouth packing firm Tri-Wall, said the firm spent around £16,000 a year on bridge tolls.
He said: "It causes us to incur extra costs, and sometimes deflect our transport company to travel in a different direction.
"We sometimes have to return from the south-west of England via Gloucester instead of crossing back into Wales."
The UK government said there were costs it may have to recoup even after the bridges reverted to public ownership.
In a statement, the Department for Transport said: "No decisions have been taken on the future management or tolling arrangements of the crossings after the end of the current concession.
"However, the government has been clear that any future arrangements will need to make proper provision for repayment of government costs, future maintenance and reflect the needs of road users in both England and Wales.
"We are not proposing any changes to the ownership of the crossings at this time."
The Welsh government has called for control of the tolls to be devolved to Cardiff Bay.
Sunday Politics Wales, BBC One Wales, Sunday 2 February 11:00 GMT
Cross-party calls have been made for the Severn Bridge tolls to be cut drastically when the UK government takes control of charges after 2018.