I've just had an estimate from MEA for a bit heavier service, 26 poles required, 500kVa / 24 kV, 416/240 V transformer, 3 phase, 70 sqmm cables hv side, 185 sqmm lv side, includes all necessary tray panels and switch. Fully installed price including VAT 3.211 million THB. 120 days to install. Maybe gives you some comparison basis. Good luck. Could be apples and oranges as few details on your installation.