Why not look around your neighborhood for seedlings and try with some of those?
In my area you can find seed and seedlings from maple, oak, linden, cedar (arborvitae) and the odd mulberry just by walking around the parks. Your area should have a different but equally interesting selections. A bit of quick work with a trowel and a plastic bag and you have bonsai material at no cost, and no guilt if it should die.
Some trees are better bonsai subjects than others. The criteria include
- diminution of leaf size
- mature bark features in a young tree
- whether it will flower as a bonsai
- ease of shaping to a style
If you wanted to try tropical bonsai that would stay indoors all the time some easy options include
- boxwood - outdoor plant can be kept indoors- start from cuttings or buy a plant
- citrus - orange and grapefruit trees sprout easily from seed
- jade plant - should not need wiring - easy from cuttings or leaves
- date palm -easy if you start with fresh dates
- ficus family - ficus pumila would be easier with it's small leaves but the common ficus from a tropical plant store has possibilities
- Podocarpus macrophylla or Buddhist pine - nice plant - harder to find - sometimes available from tropical plant suppliers - nice bark, leaves get a little smaller, easy to train
- ming aralia- beautiful plant for indoor bonsai, leaves are proportionate to the pot size, bark goes gray early in it's growth, buds from old wood