Stepping stones or crushed gravel might be the cheapest options otherwise you might have to hire one of those machines to compact the earth and make the surface even.

Make sure you prepare the foundations well by removing all weeds and laying something down to prevent weeds from coming through.

make sure you have weeds in control so they won’t grow underneath and around.

My kids made their own.. We found containers big enough, mixed cement and mixed in the colour. Placed pretty pebbles and marbles on the bottom then poured the concrete on top and let it set.

We did a simular idea in our previous house using cheap 20 by 20 pavers, even with putting crushed rock and sand below two years later they became uneven we did it ourselves but wish we spent a little extra once we had the area cut out and ready to go and hire something to compound the sand and rock to make it even, before laying he pavers. we just used a old fashion heavy concrete roller and eventhough we thought we had done it right it become uneven after settling, a days hire of the compounder(or whatever they are called) to even out he sand etc would of saved us having to redo it two years later.

Checkout youtube and Bunnings websites they can show you DIY projects which will show you the way plus tips.