I have a cheap solution to filling these beds with "soil." Use the lasagna method. Start with cardboard from scrounged boxes. Then later with lawnmower shredded leaves, layers of wet newspapers, free coffee grounds from local Starbucks, more shredded leaves, any other kind of nitrogen rich waste such as chicken manure that I get free from hobbyist. All this is free. Layer it good and high and let the winter rain do its job breaking it down. You can plant into it after 2-3 months even if not all is broken down; it's like raising your seedlings in a compost pile and it works great.
