Been through this airport 50+ times and watched tourists get fleeced. The gate area restaurants charge ฿400 for pad thai that costs ฿60 outside.

Go to basement level food court instead. Same quality, local prices. Kao man gai ฿80, green curry ฿90. Cash only but there's an ATM right there.

Free shower on 4th floor domestic side if you're gross from a long flight. Towel costs ฿50 but worth it.