I'm not sure why you'd have to pay for used coffee grounds, but Starbucks is giving away their coffee grounds for free, to be used in your garden. I say, just use your own and avoid that place altogether, but here's some stuff from their website:

Coffee grounds can provide a valuable source of nutrition for your garden if used properly. The proper amount to be used depends on the condition of the soil and, more specifically, what you are growing in your garden. Check with your local gardening expert to see what is best for your situation. Here are a few general tips:

• Applying coffee grounds directly in the garden. Coffee grounds can be applied along with other materials as a side dressing for vegetables, roses, and other plants. Coffee grounds are high in nitrogen, but are also acidic. Adding brown material such as leaves and dried grass to the mulch will help keep a balanced soil pH.

• Mixing coffee grounds in your compost. Coffee grounds act as a green material with a carbon-nitrogen (C-N) ratio of 20-1. They make an excellent addition to your compost. Combined with browns such as leaves and straw, coffee grounds generate heat and will speed up the composting process.

• Using coffee grounds in a worm bin. Worms fed with coffee grounds combined with other materials will flourish.

Whats in coffee grounds? Starbucks commissioned a study in 1995 to better understand the make up of the organic matter we call coffee grounds. The following is the result of an analysis of our used coffee grounds performed by the University of Washington College of Forest Resources:

Primary Nutrients

Nitrogen 1.45%
Phosphorus ND ug/g
Potassium 1204 ug/g

Secondary Nutrients

Calcium 389 ug/g
Magnesium 448 ug/g
Sulfur high ug/g