With soil you need to be a contrairian or Do the opposite of what it is

Sandy soil needs something to hold water
clay soil needs sand to dry it
wet soil needs something to dry it (grit)
poor soil needs something to enrich it (compost)

I wouldn't spend money on trying to enrich a large plot. I'd look for maybe a farmer or small holding that has waste from cowsheds or horses they want to get rid of and then dig it in over winter. It needs to be rotted down before use but time is free. Also make compost bins with old pallets and compost everything you can.