G - God's
R - Riches
A - At
Grace is simply 'God's unmerited favor towards you.' His grace gives you kindness though undeserved. He has riches for you. His riches will satisfy your deepest needs.
Like every good thing, His riches comes with a price. Fortunately, it's a price which you don't you have to pay. He has paid it himself. Christ was hanged on a cross as a price of all God's riches for you.
The only thing you have to do it is receive it. Just like you would receive a gift from your loved ones, you can receive God's gift.
Grace is the most expensive thing you can have in your whole life, all free!