|That's an easy question to answer. None. |
Wi-fi only has a maximum range of around 100 meters, often less.
Even with a high gain omni-directional antenna you are not going to get 3 kms. You might just do it with a line-of-sight connection and both ends using directional antennas.
For long range wireless access you need to be looking at WiMax and that can be expensive.