Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Townsville to Reykjavik as you normally would.
For a flight from Townsville to Reykjavik, you will be flying from Townsville. Townsville (TSV) is just 4.5 km from the centre of the city. Townsville is the only Townsville airport and it handles 0 outbound flights to Reykjavik per day. 0 airlines have flights to Reykjavik from Townsville on a regular basis.