Torque wrenches tend to be pretty pricey across the board in my experience, but getting a 5/16" one for SMAs used can be more reasonable on ebay and the like. Something like the Huber & Suhner 74 Z-0-0-21 sometimes has some availability on the used market for around double the price you're looking at - $50usd or so.
Otherwise even for torque wrenches for other fields, they tend to be quite expensive when new, so you run into the same issue on the used market. Something like the Anritsu 01-201 can come up on the used market and if SMA isn't marked in the title you may be able to get it cheaper (and fewer people will see it). Also worth looking for Wiltron branded wrenches, since they're the same but just from before Anritsu's purchase of them.