In a Tau army this size, you need a key devestating unit.
Drop the sweet stuff (upgrades) and keep the suits cheap.
Keep you Troops effective, but not expensive (8-10 Fire Warriors are great, Shas'ui and 'Fish are scary)
In games this size (and smaller) Ive had huge success with Stealth Teams.
A team of 4 is cheap, hard to chase and pack a huge amount of shots.
As for other effective bodies, cheap kroot (any size -no shaper required) and Sniper Teams (3 AP3/ Pinning weapons) work well. Vespid are also great, AP3 weapons, fast and relatively cheap.
Obviously, Im not sure what models you have available, but target saturation works very well for a list this size.
With Tau, they need to focus on a unit and remove it from the board. Do this every turn. Find something you dont like the look of, and kill it. All of it. No survivors.