Amazon Warehouse (used) frequently has Amscope products starting under $100. They come in a huge variety of configurations, so it can be daunting figuring which models are best. I use one for soldering, so the size of parts and tools is similar to watchmaking.
The first link below only has a 2" (50mm) working distance, so it may be difficult to get tools in. Would work great for inspecting parts, less so for working on the movement under the scope.
The second has a 9" (230mm) working distance so it would be suitable for working on the movement under the scope.