Did you check the Special Offers tab on the website? Garuda promote a lot of good fares there. As per my experience, lower fares tickets on Garuda should be purchased in advance rather than later. Garuda don't usually release cheap fares closer to the date of travel.
Cheap might be relative, if the only experience the OP has is checking GA prices overseas.
At CGK last year, I bought a one-way CGK-PLM ticket for US$65, two hours before the flight. The highlight was finding out that the airport tax was already included in GA tickets (as has already been mentioned).