If you're interested, 3mx units come up on eBay every so often for £60-£100. Classic S3 and 3a units are a lot more common, though, and are closer to £35 - cheaper if you're happy to fix the hinges yourself.
Alternatively, MAME emulates EPOC16 machines almost perfectly.
If you're OK with Discord, we've got a friendly little community that can help to get you going, including with connecting EPOC16 machines up to modern OSes.