Does you’re local nursery sell truck loads of soil? I have found this to be super affordable. Ours sells one scoop (which fills a pick up bed) for 14.99. It has garden soil and compost in it already. I just add some

manure and I’m good to go. if that isn’t an option I have found Kellogg organic gardens soil to work well too. I can find a 2 cubic foot bag for 7.57.

There is a difference between a raised bed and a large container, and it makes a big difference in the growing medium.

• A container is a completely enclosed artificial environment. The container has little access to the actual soil and all the diverse ecology that lives there. Everything it needs has to be provided by you.
• A raised bed is a garden with sides to which amendments have been added. It is connected to the natural environment with earthworms, beetles, fungus, bacteria, and everything else that interacts with the soil. It can be organically pretty much self-sustaining, if you choose.

What you have here leans more to the container side of the equation. It has a bottom. It is essentially a big pot.

Because of that, I suggest you look at filling it with a container / potting mix. Also, treat it like a pot and use synthetic fertilizers. You can't count on the right biology being present to break down organics into simple nutrients that the plants can take up.

Another reason to avoid actual garden or topsoil is that I doubt that this fabric could take the weight and pressure that actual soil would put on the fabric year in and year out. You want something lighter that won't rip the sides.