I think this is the cheapest 250/25Mbps plan that I can find for Opticomm fibre.
You can also get 100/20Mbps for $80 and get the same free activation and free router (NetComm NF18MESH)
P.S: This deal is for Opticomm Fibre areas only and NOT valid for NBN areas.
For NBN, check this deal instead.
Spoke to their staff and they said the price will not go up as long as you stay as their customer, but could not find the information anywhere else on their website.
If you decided that you don't like them, the cancellation fee is $100, which is ok in my opinion.
Screenshot of the checkout page: