SoftUK is selling "Rome Total War Gold Edition" for the PC for £7.99.
You can get free delivery by entering the code "cheap games" (without quotes).
A few sites will give cashback on top of this (e.g. 2% from FreeFivers, making it £7.83)
Th next best price seems to be £13.99 from dvd.co.uk.
The Gold Edition contains both "Rome Total War" and the "Barbarian Invasion" expansion pack.
Total War Gold Edition brings together the multi awarding winning Rome: Total War and its critically acclaimed official expansion, Barbarian Invasion. Available in one great value offering, this is the perfect opportunity for armchair Generals to conquer and control the greatest empire ever known by man. In Rome: Total War you must guide one of three noble Roman families on a century spanning quest to seize control of the Roman Empire. In Barbarian Invasion witness the decline of Rome as it come under attack from Barbarian Hordes and a bitter internal struggle between rival factions.