For a small mini excavator, a maximum of 100€/day should be charged.
And what is the mini excavator supposed to do? Have you ever tried to spread 100m³ of soil with a mini excavator? A 15t excavator can easily accomplish such a task mentioned above in one day, a mini excavator will probably need a week for that. If the existing topsoil still needs to be stripped beforehand, even the week won't be enough. Even though nowadays everyone can rent a mini excavator and a wheel loader from the local rental company, in many cases it absolutely doesn't make sense. For jobs where you want to move a lot of soil, you should ALWAYS use the largest equipment possible. This is usually also the cheapest option. The excavator operator costs the same regardless of the size of the machine.