SAINTS will have to pay Brentford an initial £125,000 for Ryan Dickson, after a tribunal set the transfer fee this afternoon.
But that sum could double after a number of add-ons were included.
Saints signed the 23-year-old left-back on a free earlier this summer, after Dickson rejected a new deal at Griffin Park.
However, as he is under 24, Saints are required to pay compensation.
The two clubs could not agree a fee, with their valuations some distance apart.
Saints were understood to be offering about £100,000, while Brentford initially wanted half a million.
The Bees were confident they would receive at least £300,000 at a tribunal.
But at most they will receive £250,000.
Saints must pay an initial £125,000, but will have to pay £25,000 when Dickson plays 10, 20, 30 and 40 competitive first-team games for the club.
They will also have to pay a further £25,000 if they achieve promotion.
So, if Saints go up and Dickson plays the majority of the season, the deal will almost certainly cost Saints £250,000.
A 20 per cent sell-on fee has also been included.