Hi Uroarz,
Salomonander is right.
What you are offering doesn't make any sense at all, I really think of you are bored and need to learn and experienced you should do a List of all the professional studios in a 30Km radius from your location and ask for an internship. No more boredom and you will learn a lot and enjoy the experience, then you will also learn a lot how to value your work.
It's not really that I think you will dump anyone's prices, I couldn't care less about that because someone that offers those prices also offers a service of the same value.
Every time some musician says to me a friend will mix their record for free then I already know the mixes will be crap and in the end they will pay me my normal fee to mix it .
So if you want to do that, thats fine do it.
You will soon learn how much time and effort it takes to mix, you will learn your limitations and you will feel low self esteem when people will not want to use your work because the mixes were crap.
Also most serious musicians will not fall into a type of offer like that, they already know that quality doesn't come for free, so the bands you will get will be pretty terrible stuff and really badly recorded.
So you will work for free in really bad music and miserable audio, good luck.
Like Salomonander said, if you want to work for free better to offer that to a studio and become an assistant there.
Regards