For low power applications, Arduino boards are out. They are just not designed for it. There is ancillary circuitry that continues to draw more power than the microcontroller even when the MCU is sleeping. This is not a criticism, they are designed as prototyping boards.
This means that you are looking at a custom circuit and possibly a custom PC board.
I haven't used any of the various WiFi modules but my perception is that they're not necessarily designed with low power in mind, i.e. may not have a sleep mode.
This seems to me to be a perfect XBee application. On the one end, sensors, a microcontroller and an XBee. On the other end, either (a) just an XBee connected to the computer, or (b) an XBee and a microcontroller. Depending on what kind of programming you want to do. Not sure if it's important to your application, but if having a computer running all the time isn't necessary or desirable, a microcontroller on the receiving end could store the data on a micro SD card, for instance.
I'm sure that a properly designed sensor board with an XBee and an ATmega328P microcontroller like used in the Arduino Uno (and others) could run maybe six months on a pair of AA alkaline cells, transmitting data once every ten minutes, and sleeping the MCU and the XBee in between. Assuming that the sensors themselves are not terrible power hogs or need to be powered on for relatively long periods.