@phangmoh I am using IMST iC880A + RPi which is running at 868 MHz. I bought this gateway before MCMC decided to remove 868 MHz band from SRD category in 2018.
The only band that we should use now for LoRa is 919MHz - 923 MHz. So, if you are planning to buy a new gateway from RisingHF, then 915 MHz gateway is the only option to go.
The idea of TTN is to provide a free IoT network which is community owned. If your sensor nodes are connected to any TTN 's community gateways, then it should be free even it is in Malaysia.
Hope this helps.