The valuation represents a multiple of 0.84 times 2006 revenues.
The deal does not include Trinity's North Surrey and London division, which houses titles including the Fulham Chronicle.
Sir Ray Tindle's Tindle Newspapers owns around 35 local titles including the North Cornwall Advertiser and the Abergavenny Chronicle.
The deal is the latest in a number of regional newspaper disposals embarked on by Sly Bailey, Trinity Mirror chief executive.
Last month, the company sold its Berkshire Regional Newspapers Group to Berkshire Media Group for £10m and 25 of its south-eastern regional papers to Northcliffe, a division of the Daily Mail & General Trust, for £64m.
It is also in the process of selling the Racing Post and its sports division, and expects to complete this by the end of September.