Most people I know that actually use ChatGPT, use the free (GPT3.5) version. Not a lot of people are willing to pay the extra 20 euros per month.

Yet, if you want to go cheaper, you totally can by paying for the API access. Gpt4 is accessible there and you get to use your own app. $20 will last you way longer then a month if you're not a heavy user.

It really depends on usage. If you need to have long conversations, or are sending huge texts, the all-you-can-eat for $20 plan will almost certainly be cheaper than API access.

If you're doing lots of smaller one shot stuff without a lot of back and forth, the API will be cheaper.

True. Though I myself still use ChatGPT a lot more as I can quickly reach the $20 threshold via the API

Do you think it's getting close to the point where it adds a euro of value per workday (on average) for them?

Depends on if they know how to use it. A lot of people still think it's just a google and wikipedia replacement. It doesn't really do anything super useful in that case.