It is not all super expensive, but definitely not as cheap as the US. A lot of stuff is localized and compared to the big name imported stuff (assuming you can find it) is relatively cheap. For example a 20L bag of bark compost for $3.
For comparison to Promix, if I were to mix my own: 100L of coir would cost me about $10, 15L of Perlite probably about $6, and 10L of Vermiculite is about $4. So $20ish for the base mix, then maybe another $15-20 or so f...
Crazy! I saw some really awesome vertical growing planters posted on facebook from a guy in Japan, hundreds of plants, wonder what he used. Guess he probably made his own. Cause promix would have costed him thousands for that much lol