If you don't count the radio that comes with a new car?
Early 2000s. Maybe 2002-2003? But it wasn't me just buying a radio. It was 10, and I didn't pay for them. See, I got a part time gig working with Media Monitors as a "recording engineer." They had people in major/large markets who would record radio stations so they could track the ads. They'd have a set-up where the "engineers" would record stations on reel, package up the tape and send it back to the company so they could crunch the numbers.
I'm fairly certain that I got the first or at least one of the first prototypes of the digital version. A desktop computer, audio interface (MOTU if I remember correctly) and we (me and the guy who set it up) went and bought ten little transistor radios. Tuned them to the stations they wanted to track, plugged them into the system, and launched the software that would record them on a set schedule. I'd adjust it when needed, would burn the data onto CDs, and send it off via FedEx. The very modest checks would show up later.
I think I did it for maybe a year before they figured out a better way to do things and I packed it all up and shipped it back. I never really made all that much money, but I did get a very nice desk for my office (with some rack space) out of the deal. Just a funny little corner of the radio business...