After a lot of work, I've got a pretty good raspberry pi setup working with a $20 RTL-SDR dongle.
I've been testing this at home with a rooftop antenna to a private icecast2 server and I'm getting pretty good results, so I'm moving it to our club hangar at KMAN later this week. Then once I'm happy with the antenna situation I'll move turn off the scanner feed that I'm using for KMAN and use this.
Here's a picture of the insides. It's all powered by a single ethernet line, which has a power injector that goes inside, followed by a lightning arrestor that hopefully will protect the indoor equipment if the enclosure is struck. On the inside of the enclosure, 5 volts is grabbed from the power over ethernet splitter and used to power the pi. The DRL-SDR dongle plugs in to USB and has an antenna connector that is routed outside.
I'm running a modified version of rtl_fm that I made that has a built in audio AGC and squelch. It demodulates the audio and pipes that directly to the ices2 app, which streams to an icecast2 server. It only uses about 15% of the CPU time.
This is the external enclosure with the cheap RTL-SDR antenna. I'll likely switch to a 8db gain VHF antenna, but I wanted to try this first.
The pi itself has a 5 megapixel camera, which I'm grabbing stills from every 15 seconds, downloading and overlaying the METAR, and uploading to a webserver. This is just a sample capture out my window last night.
Once this is running I'm going to work on a custom app based on rtl_fm that supports 2 SDR dongles at once. Then it will use the squelch code to combine a UHF and VHF feed into one stream, so you can get ATC audio from both frequencies on a single stream.
The total cost for this setup is about $200! No scanner or audio ports are needed.