When you're talking about crossing and developing new plants, you're getting a little bit out of the realm of gardeners trying new plants.
Gardeners do try new plants…… rather they try new varieties of garden favorites that are sold by big box stores….. think of all the new coleus varieties that are introduced every year.
When you're talking about private gardeners developing new varieties, well, that's another thing.
Many now famous hybridizers of plants such as roses, day lilies, etc did get their start in their own gardens, and some worked for years before their creations were recognized by their respective plant societies.
The best way for a private gardener to get into the world of creating and selling new plants is to start slow and local. Sell the plants to the gardeners in your area. Then, as Bob says, go on the net, through Etsy, Amazon and the like. Build a good reputation there.
Unusual plants can be a fad thing, a trend, as evidenced by the now huge prices for variegated philodendrons, hoyas and the like. And a lot of vendors selling these plants are getting on this bandwagon, and selling these plants as cuttings that have no chance of survival, as evidenced by the large posts on ask a question and also on the philodendron thread, so if this is the intent to develop unusual plants and then sell them online, one has to consider what's hot and what's not, plus make sure that what one is selling is guaranteed to grow.
Otherwise, just develop new and unusual new plants for your own enjoyment. What you're really trying to do determines what direction you take.