Cloud Tank/Airship/Airballoon?/Blimp??/Convoy

[GooglyBoogly]

I'd put it in the 1-1.5k range. All of the beginning tanks are ground, so maybe at least one more air besides heli would help.

The helicopter costs 1k and 1k is within the 1-1.5k range.
You want an air tank at the beginning - we already have the heli tank, and it does a good job.
We also have the trader, another air tank that can be purchased with starting gold.

The hp/$ formulae is pretty much set, so unless you have some revolutionary idea for a new tank that requires it to be air, and would be useful at low lvls with low $$ needed then I think you are out of luck.