Tau's not really set up for low points though, on account that their basic troops is pretty bad compared to crisis suites.
But can you build yourself a HQ for 110 points with +2 armor save, +4 invulnerbility save, FNP, and two extra wounds from shield drones?
I find that my tau work great in 800 and upwards, while my necrons are rather craptastic below 1500.