Sacrifice What???

1 Chronicles 21:24 "I will not ... sacrifice a burnt offering that cost me nothing."

Reading this verse last week reminded me of a time in grade school. A friend of mine was catholic and was talking about Lent. She was telling me about how she had to give up something for the week. So she decided to give up chewing gum. But then she shared that she liked gum - so it counted - but she only chewed it once in awhile so it would be easy to give up for the week.
I didn't understand it then, now I do. She was living by the letter fo the law - giving up nothing.
Christ gave up his life for me. Can I don anything less for him? What does it cost me to worship God? What can I give up as an offering? Will I be like David and only offer something that cost me or more like my friend from school and offer up something that costs me nothing?