It depends what you want to use it for. Not only how accurate you need it to be, but what the range is. Torque wrenches come in various ranges, and you want to be in the middle of the range for the most accuracy. You also want to use a wrench with an appropriate sized drive for the sockets/fasteners, so that you aren't risking damage to the wrench attachment (if it's too small) or the fastener (if it's too big).

For torquing anything into/onto carbon fiber or aluminum, I'd shell out for a good torque wrench. I have a cheap Craftsman 1/2" drive beam wrench for the rear axle nut on the motorcycle. I have a Snap-On 3/8" drive click wrench for most of the mid-sized fasteners on the bikes and cars. Then I have a Consolidated Devices 1/4" drive click wrench for in-lb fasteners like valve cover bolts and anything on the bici.

A good torque wrench will last you a lifetime and potentially pay for itself many times over in damage prevention. It costs about the same as two pairs of cycling shorts (one pair of expensive shorts!) or two sets of tires.