Here's what I'd take:
Ethereal
3 Crisis Suits w/ 2xMissile Pods, Flamers
10 Firewarriors in Devilfish w/Disruption Pod
10 Firewarriors in Devilfish w/Disruption Pod
Hammerhead w/Submunition, Smart Missiles, Disruption Pod
That leaves you about 15-ish point to play around with. This should do reasonably well against most lists you'll see at this level. You may consider swapping the Hammerhead for a Skyray.
There's a lot of different lists that can work at 750. The Tau are spoiled that way.