RF module suggestion wanted

I want to make two Arduino boards communicate over distances of up to 1 Km. Due to the application I will need to us RF transceivers that communicate over the 2.4 Ghz band and support Direct Sequence Spread Spectrum mode. I expect the Arduino to communicate with the RF module over an SPI, but would prefer not to use an XBee device since I would like more control over the protocol. So far I have only found the AWA24S by Artaflex, but it is a bit pricy.

Can anyone suggest an RF module that fits these requirements?

20 to 30 dollars/euros is what I would expect of such a module.

Why do you need such specific communication. Do you need to transfer a lot a data ? With a good directional antenna, only 100mW is enough for 1km. More power is forbidden in many countries.

My hope is to build a radio control set for a model aeroplane. To fly this in the UK requires the use of 2.4 Ghz and DSSS (or other bands and swap the crystal so as not interfere with other flyers). I am currently planning to send a packet containing control data every 20 ms and put measurements from the plane in an acknowledgement packet. I have no experience of RF communications (or of building anything 'real' using Arduino boards), so I am trying to research the options and experiment with a UNO board.

The AWA24S costs about £20, so I guess that is about right.