Fair enough. You may be able to make your own slim ‘enclosure’ with a couple of end caps, an o-ring, and some CNCing to make room for a non depth-rated bullseye level but, factoring in tool requirements and design time, that could end up costing the same or more than the expensive ones you’re trying to avoid.
Hopefully the community can post some alternative options/ideas, but I’m not sure how common an application like this is.