Welcome to the community, @Aurelien_G! :grinning_face_with_big_eyes: As you’ve discovered, value ranges aren’t allowed in currency or number fields. The best you can do is enter the start and end values of the range into separate fields. If you want to see those combined into a single field, a formula will allow you to do that, though you’ll run into another fun fact about Airtable: while there’s a function for formatting dates, there isn’t one for formatting numbers. The formatting that you see in currency and number fields is there for display purposes only, and doesn’t get passed to formulas that read those fields.
Long story short, if you want your currency/number values re-formatted, your formula will need to take care of that. There are discussions on number formatting elsewhere in the forum, but there’s also a really slick app called “Ready-Made Formulas” by @kuovonne that contains lots of formulas for specific use cases, including number formatting.