Until you have funds would you consider a wild life area, they are relatively easy to make, decaying wood, stones lumps of concrete, maybe a small tin bath for frogs and toads.
I would plant cheap plants some in pots and some in the ground. Do nt dead head them as the seeds will grow again. You need plants that have a shallow root system and a spreading habit lamium, dead nettle is perfect also periwinkle and forget me not.
A good tip for planting on stony ground is to take the bottom of a plastic container. Fill with soil, Then plant invasive plants which will make there way to rough ground underneath. Don’t use good quality soil for these. Japanese anenome , Astilbe, Cornus, Cocnurnianius, white stemmed bramble, forgetmenots,acqueligia, ladies bonnets, bleeding
heart and astilbe. They are tough as old boots..
To disguise the plastic place stones and wood around them for the insects. They will gobble up the falling leaves.
A excellent place for cheap plants is Wilko. They do ivy, heathers, low stealing cypress plants and ferns.
Hope this helps