Soil Question (Sandy and Thin) New York

Hey guys, Im a new grower and had some newby questions.

I had a question on my native soil. Im doing a outdoor grow in my backyard woods and found the soil to be very sandy. Its thin and has lots of decomposed leaves, roots, etc in it. I was wondering what would be a good and cost effective way to mix/improve the soil. Im looking for something inexpensive as I want to grow a lot of plants.
Also what is the latest you would could plant and still have the plant be successful?

another NY grower here, this time of year is plenty early, been frosts for the last week, those didn't help the early growers
for organic stuff on the cheap, composted cow manure is good for this

Its supposed to get warm though which is a plus. I figured I would start planting this week and do as many as possible until june. So Il get composted cow manure, should I get anything else with it to? Like pete moss or bonemeal?

peat moss is good, so is bone meal but it attracts animals of the digging variety - outside fertilizers that don't attract animals are the trick