Docedison:
And the same module here for $2.75 US (this price is typical of many vendors on Ebay) 5.50 Ea should be for a pair... Check it out.
[price-up] NRF24L01 2.4G Wireless Module, Genuine Chip – ElectroDragon.
I recently bought 6 of those devices and a USB Receiver "Dongle" for $9.95... "Free Shipping"... Too ? $22.00 Ea... Yeah I'll Bet... that they would love to sell a bunch at that price, oh yeah and the Features on the $22.50 board are built into the Chip. All of the nRF24XX series Ic's have those features... They're part of what drove the original design and that was an inexpensive Chipset that could co-exist with all the other ISM stuff as well as Microwave Ovens @ 2450 Mhz and most capable of 1000 watts or more @ ~ 2450 mhz as the ovens use a "Power Oscillator" (A Klystron of Magnetron tube) neither of which has any external frequency control (Oscillating Frequency is set by internal cavity dimensions primarily).Doc
That $2.75 one doesn't look like the + model that sales for $5.50 at the other place. The + model adds a few features including a slower transmit speed for increased range and less power usage.
However you are correct they are cheaper on ebay http://www.ebay.com/itm/2PCS-Arduino-NRF24L01-Wireless-Transceiver-Module-/270977894613?pt=LH_DefaultDomain_0&hash=item3f178a88d5 is a + and 4.10 for 2 of them, so only $2.05 each free shipping.
Although I'd probably buy this one instead: nrf24l01 for sale | eBay a little bit more expensive but it's located in the US, so would get here 3 times quicker lol.