There is no flat 4 Baht / kWh rate, you will be on the tariff 2.1.2.
Anyway, a Schneider 3-phase board, dependent upon the number of breaker positions, is going to run to 5-10k for the board, 150 for each single-phase MCB and 3-4k for your 100A incoming MCCB.
Your sparks should be able to size the board for what you need and future expansion.