What's the cheapest way to link a few microcontrollers wirelessly at low speeds over short distances

XBee & XBee Gateway XBee - WiFi
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What’s the cheapest way to link a few microcontrollers wirelessly at low speeds over short distances.

I’m looking to keep it ultra-cheap, use common discrete parts and keep it physically small. I don’t care about bands and licensing so long as it works.

802.15.4/ZigBee, Bluetooth and WiFi all require an expensive coprocessor, so aren’t an option.

Alternatively, are there very cheap radio modules available to hobbyists? The kind of things you find in car keyfobs and wireless thermometers, perhaps?

Would building a simple transceiver on a homebrew PCB even be practical, or will I be plagued by tuning, interference and weirdy analogue stuff?

Could something like this be driven from a microcontroller? http://www.kynix.com/Product/Cate/35.html

What about receive?

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Post has been re-categorized.

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The problem with what you are looking for is that you would still be required to pass FCC or other regulatory approvals which are very costly. Up around 10K. Instead, using a simple UART connection to send and receive data wireless can be done using the XBee 802.15.4 modules relatively cheep.

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I have solved this question.