Bonsai
I think there is a fundamental cultural issue with Bonsai in the USA. As a culture we prefer quick, fast, cheap, immediate, kinds of responses and activities. Bonsai by definition is a VERY long term activity that will only appreal to a select few. Ebay does have a lot of choices for the budding bonsai artist. As you might imagine, most of the plants for sale are identified as starter plants. In other words, you get to do all the work. However, I see a few genuine old plants offered for sale too. Buying one of those would give y ou a jumpstart. However, as you can imagine, they sell for a substantial premium.
Ebay sellers also offer an assortment of Rocks, fossils, minerals, tools and books that may be helpful for creating an attractive display and learning how to care for your bonsai.
Looking at the bonsai plants reminds me of what harsh conditions plants can survive. When I was in graduate school many years ago one of the other students put a temperature recorder out on a mountain slope in north central New Mexico, USA at approximately 11,000 feet above sea level. He found there were only 11 nights all summer when the low temperature didn't get below freezing. No wonder you can find tiny trees a few inches tall that are 50-75 yerars old.
The list below shows current Ebay auctions for bonsai related items. If you are new to the suject you can learn a lot from reading item descriptions written by knowledgeable sellers. If you are searching for an established plant you can probably find one of them too. If you see something interesting the link will take you directly to that auction on Ebay.