Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Bangkok to Brno as you normally would.
Brno Turany (BRQ) is the airport you will fly into if you book a flight from Bangkok to Brno. You should not have trouble finding flights to Turany from Bangkok; the airport handles an average of 0 inbound flights from Bangkok per day. You should also have plenty of airline options to choose from since 0 airlines have flights to the Brno airport from Bangkok. It is only a 8.0 km journey from Turany (BRQ) to Brno’s city centre.