Yup if you are planning to sell mixes without the label's/artist's copyright permission then expect to get a major fine. When I was working back in the record shop, some customer come in one day and was telling me about how he done a house set with a load of Ministry Of Sound releases on, and he sold copies of the mix. They found out about it and he ended up paying about £10,000 to Ministry.
If your releasing and making a profit from anything with someones copyrighted material on it, be it a CD, DVD or anything else, you need permisson no matter who you are. Its only fair really as without doing it your taking 100% of the profit for whats only 50% your work.