Important underground pics for PhD research. Stitch photos for wide angles or use a wide angle lens?

Given what you've said, I'd opt for the wider lens. It's the simplest solution. If you're worried about the cost, buy it secondhand on eBay and sell it when you're finished with it. Pano photography is complicated, fiddly and requires a rather geeky disposition. If you want to capture this mysterious underground location quickly, accurately and simply, then an ultra wide angle lens would probably suit you best.