Though this may be very hard to believe, the torque wrenches sold by Harbor Freight Tools are accurate and surprisingly good quality. Get both the 1/2" and 3/8" drive sizes, no 1/2" torque wrench is accurate at lower settings like the 20 ft-lbs. you asked about. I have lots of very good quality tools but those low cost HFT torque wrenches do a great job and they're as accurate as far more expensive torque wrenches. The 1/2" usually sells for $19.95 and is often on sale for less than that The 3/8" costs even less. Both are a click style which is easier to use... they make a loud click when you have reached the desired amount of torque.
A buddy refused to believe his $90 Craftsman torque wrench wasn't more accurate but both tightened hardware precisely the same amount of tightness over multiple tests.
I've been using mine for over 15 years.