It's not that low cost but it is precise. It is cheaper than the cosine tool.
I'm thinking one of these would do just what we're looking for. Craftsman 6-1/2 in. SmartTool Plus Module Sears item #00939756000.
Just aim at the target and press the hold button. Now you have the exact angle to the 10th of a degree. It even reads in percent to simplify the yardage calculation. For aiming a guy might just mount it to a small scope and keep it in a pocket or just simply sight down the flat edge.