I've been thinking about how to do things for that project.
The Baofeng UV5R is cheap, can transmit 4W on two meters, and has a green LED that lights up when it breaks squelch.
From what I can find, the Raspberry Pi has an audio output, but no audio input.
So I propose to take the processor pin that drives that LED (The processor is 3.3V), disconnect the audio from the speaker-out jack, and put the squelch signal on that connector. Then that can go to a 3.3V GPIO pin on the Raspberry Pi, and you can decode keying from that.
Since it's driven by the processor, should we decide to protect it with a CTCSS tone, that's just a setting in the radio.
There's a microphone input, which I think expects electret mic inputs of ~10 mV, so we'll have to pad the output audio from the RP down quite a bit, I imagine. Do you happen to know what the output voltage on the RP audio is? I'd expect somewhere in the range of .7V to a volt.
You'll need to have another GPIO to key the transmitter, and we may want a relay or optoisolator between the RP and the radio.
I'll have to find the schematic and look at it, but I think it keys up when you ground the PTT line.
The radio comes with a funky little microphone/earpiece, so that gives us the connector to plug into the radio.
It comes with a charger that stands the radio up and can charge the battery while it's operating. It's powered by a wall wart
Anyway, that should be pretty simple, and do the job without going through a USB sound card, which is just another thing to go wrong. We don't really need RX audio, just the squelch signal.
Somewhere around here, I've got a serial cable to allow programming a Baofeng via computer, but it seems to have evaporated.