Theres 3/8 size torque wrenches on ebay for round about the £15 - £20ish mark which typically have a range of 5Nm to 25Nm. Just go to ebay and search for torque wrenches.
I've been pondering over a screwdriver you can get from Machine Mart which has a torque range going up to only 10Nm. This would be great for things on the bike like alternator bolts and cam holder bolts which would strip precious threads if overtightened...a lot of money though for a screwdriver!
http://www.machinemart.co.uk/shop/pr...hex-key-sets-2
HTH