This is an old revision of the document!
 Raspberry Pi 3 Model B/B+    | $30 (either model B or B+ should work fine) | 
 8GB or larger  MicroSD memory card     | $5 eBay | 
 USB Power Adapter                    | $5 eBay | 
 USB to serial RS-232 interface adapter    | $5 eBay. Make sure it is Linux compatible. | 
 Serial RS-232 null modem cable FEMALE/FEMALE    | $5 eBay | 
| Total project cost | $50 | 
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You can also choose to use a Raspberry Pi Zero which will save you some $15 from the total price, but for the sake of simplicity of this tutorial, we'll be using the Raspberry Pi 3 Model B. I've only tested these two Raspberry Pi's, but I see no reason why Virtual Modem wouldn't work with any Raspberry Pi. If you have success with the other Raspberry Pi's, feel free to let me know :)
On to the next part!