€10 gets you the cheap keyboard which leads to bad wrist positions, which can contribute to RSI and carpal tunnel.
€60-80 buys a mass-produced ergonomic design, like the Microsoft Ergonomic. These aren't adjustable or programmable, but it's easily a worthwhile improvement.
(Personally, I bought a mechanical keyboard because I don't like the low-travel laptop-style keys that are now standard on the MS Ergonomic and other similar "cheap" ergonomic keyboards.)
€100-150 buys a mass-produced, adjustable, reprogrammable (to some extent) keyboard, like a Kinesis Freestyle. This will help people with wrist issues, and will seem an obvious improvement to anyone who has a Microsoft Ergonomic. It also comes with mechanical keyswitches, which give more options in typing pressure.
€300 buys a sculpted ergonomic keyboard, like the Kinesis Advantage2. I've never used them, but people who have had wrist problems seem to swear by them. They look comfortable to use, if you know how to touch-type in the standard way.
Within this whole range are DIY and small-scale ergonomic keyboards. The price varies a lot depending whether it's self-assembled, self-printed/cut, etc (this obviously makes no difference to the effectiveness of the keyboard), the type of key switches chosen (this makes some difference, but will eventually lead to the kind of discussions one hears about 99.999999999% copper speaker cables where people are spending €2+ per switch) and the key caps (which is 99% appearance).
All of them are fully programmable, and there's potentially a lot of customization possible for tilting, positioning and so on.
The key switches and key caps are independent from whether the keyboard is ergonomic or not, so you can also spend €300+ on an extremely un-ergonomic keyboard with just 50 keys, a milled aluminium case, 8° tilt, no feet, €2 switches and incorrect Japanese key legends with colours taken from a manga. This should be considered art rather than a useful tool.
Adding the €150 Japanese key caps to a €120 kit-built ergonomic keyboard doesn't make it worse, but mine looks good enough with the plain €15 key caps.