TRANSFORMING junction 10 of the M5 from a two-way into a four-way junction would cost more than £13 million, it has been estimated.
The bid, backed by an Echo campaign, was prompted more than a year ago by plans to replace the junction's 40-year-old motorway bridge.
The Highways Agency has calculated the cost to upgrade the busy intersection would be £13.2million.
But the authority said its feasibility study had shown the remodel "would not have an overall benefit to the road network in the local area at this time".
There are currently plans in the pipeline to spend a similar sum to repair the Piffs Elm Bridge at the junction.
Tewkesbury MP Laurence Robertson, who has been a leading advocate for the transformation project, believes the two pieces of work should be done at the same time to minimise disruption.
He said: "I am campaigning for this and I want to see the minister again to talk about this issue.
"Now we have that figure, it is about trying to move it forward. It is an ideal opportunity to remodel the junction while the bridge work is being done.
"Obviously there are a lot of businesses in that area and they would all benefit while the new fire station would be able to access the motorway southbound.
"It would also take pressure off of other junctions.
"It could all be done at once – doing it separately five or 10 years later would be wasteful. Also, doing it at the same time could mean a possible discount."
Highways bosses have set out a timetable which would see the bridge work carried out in the spring.
The Department of Transport had initially insisted that the Piffs Elm Bridge could not be repaired, only replaced.
But it has since backtracked, saying innovative working techniques will allow for repairs after all.
The road will not be closed to traffic while the work is done, but delays are expected as the work goes ahead. The bid to turn the junction into an "all movements junction" has been backed by businesses who say doing so would increase trade and prevent unnecessary journeys through Cheltenham.
David Owen, chief executive of Gloucestershire Local Enterprise Partnership, said: "Gloucestershire's Local Enterprise Partnership is in favour of firmly advocates four-way access at Junction 10 of the M5. Gloucestershire thrives on logistical advantage – its ability to connect customers with markets and we see Junction 10 as a significant issue.
"We shall continue to exploit the LEP's direct line to Government and national media to put the case to secure business growth through infrastructure changes."