You pay for the geometry - JP Enterprises 45 Degree Offset Adaptor

This mount's claim to fame is to center the pic rail over the bore axis, and it does it. This isn't so important for many accessories, but is desirable for back-up sights/optics. It's low enough that it would likely be on the same plan with absolute co-witness height optics when rolling over to 45 degrees which makes for a seamless transition. If your main optic is higher, you can always add a spacer. Getting lower is the harder job. It's a pricey little piece, but there aren't many out there that are fit for this purpose, so I figure you are paying for the engineering. I'll use this for all my offset BUIS etc applications in the future.