tonya, the best thing to improve your soil is huge amounts of organic matter. Preferably compost, but manures, leaves, grass clippings etc will all add to the soil. Don't buy in a heap of garden soil, it'll just be lost into the sand. See if you can get a few cubic yards of compost delivered. More is better. You can add as much as 10 inches or so deep over the area. It needs to be aged if it is manures or grass clippings. Also, always mulch your soil. This will add more organic matter slowly replacing any that leaches away.
Consider starting your own composting system. Doesn't need to cost anything.
A worm farm also dispenses good stuff to get into your soil. Easy care pets too.
Use organic fertilisers like fish emulsion and chicken manures as well as plant
tonics like seaweed extracts. These keep the bacteria and other lifeforms healthy in your soil and help promote creation of humus. The rotted organic matter which plants
All this doesn't tend to happen in one season but just keep it up and over time your soil can be extremely healthy and productive.
Alternatively, you can always build up your beds on top of the sand using the above materials but in greater quantities. It depends what is available in the way of organic matter.