Has anyone seen a cheap unlocked or Optus smart phone?

My phone is stuffed and needs to be sent away by Optus. The last time this happened it took them 2 months to determine the phone irreparable and to replace it.
So in the meantime i want to buy a cheap phone to use and keep as back up for when my next phone dies as it's bound to happen.

I've seen so many cheap Telstra phones. Coles even has one for $29 and there are others for around $79.

The cheapest Optus phones i have seen are between $109- and $200ish.