A replacement head could easily cost two to three times what you paid for the wrench. Not all that hard to make, though, cutting the head off of a cheap ratchet and turning it to fit the body wouldn't be a problem.
I used to have a torque wrench in my hand at least ten times a day when I was working, and, yes, I own 8 of them in various sizes and styles.
$20 is pretty cheap for a torque wrench, but it should be accurate enough for the home hobby mechanic. The last torque wrench I bought before retiring was from Snap-on, and it's electronic. Cost me $375, but what I got with it more than justifies the cost....a certificate of accuracy.
None of my torque wrenches have interchangeable heads like the Utica, but in 45 years I've never needed such a feature.
Having interchangeable heads on a torque wrench would indicate to me that it was designed to be used in an industrial application, where the same size bolt or nut get tightened, all day long.
No good deed goes unpunished.