Reishi Organic 16:1 Dual Extract
The most credible source of this form that I've identified is Reishi Organic 16:1 Dual Extract sold by Lost Empire Herbs in the USA.
16:1 extract means that 16 kilograms of Reishi mushrooms are used to produce just a single gram of this extract.
The Mycelium is a part of the mushroom, which at least in the case of Reishi, contains less of the bioactive components, than the stem or the cap. It's cheaper than extracts of the cap and stem but the Nootropic or biohacking effects desired will likely be diminished.