I have the Pedros torque wrench. Specially built for the usual bike torques. I think I paid something around 100$ for it. Not necessarily cheap but it doesn't break the bank either. Well worth the money if you put a few bikes together.
X-Tools one is alright, comes with all the bits needed for work on a bike, and will do most jobs on a MTB, only the square taper crank bolts need more torque I believe.
You've reminded me I should really get one for my bikes, especially modern carbon stuff, I don't expect I'll find one for under £30 though.