About €110 for a complete kit, excluding tube
Back in the old days, when technology mysterious and needed to "warm up" before you could use it, there was a little green thing on the front of radio that told you how strong the signal was. These were "magic eyes", and they fell out of fashion, because they are hard to drive and there were much easier ways of achieving the same result. LED killed everything.
If you look around on eBay for "magic eyes", you'll find a fair umber of results, but only very few of them are full solutions.You're going to have to deal with the heater voltage, the driver voltage and mounting the tube yourself. That's no good.
Mr. Nixie has put together a kit for most Noval (9-pin socket) magic eye tubes, which takes care of the voltages needed to drive the tube, and has an automatic input gain adjustment, so you can just fit the tube in, connect it up to a supply and a signal, and you are ready to go!
If you fit an EM83 tube, (which is a stereo tube), you'll get a stereo display. Nice!