The HC-05 is what you want. They’re super cheap, in the $6-$8 range (incl shipping) even shipped from locally here in the USA. Check eBay for China-shipped units for even less. There’s a LOT of information around on interfacing with them.
I am looking at purchasing the Cobra II but it does not appear to be available with any comms except USB (unless your order 100+) . My preference was to buy everything at one place as it is not uncommon for us down under to pay $50 freight for each shipment of a $10 item
Bluetooth was my preference but might go with wired ethernet and play with bluetooth/Xbee later on.
Concerning BLE, Bluetooth SMART or Bluetooth 4.0 it must be considered that (as far as i know) those modules can not communicate with the “old” Bluetooth 2.x devices. To communicate for example with a PC a so called “Bluetooth SMART Ready” dongle is needed.