Yes you need the Arduino, an Wireless SD shield or an XBee shield. These to shields then need the XBees or WiFly modules added. WiFly have the same footprint as the XBees and give you WiFi.
However for a range of 30ft a wire connection should be ok. (Use twisted pair).
If you go the XBee route, you can connect the sensor directly to the XBee - no Arduino required. That requires a bit of configuration magic to get working, and requires using API mode to get the data on the coordinator.
If you go the XBee route, Rub Faludi's "Building Wireless Sensor Networks" is a worthwhile investment.