Let's see. Single gene. So the last single gene I bought was the enchi. I saw her picture, looked up the breeder and asked friends about him, then bought her because she was too hot to pass up. I don't remember off the top of my head how much I paid for her. I think it was $600. I don't really care because she's a female and she makes me smile when I feed her, change her water, clean her, and take pictures!
Edit: When I am deciding what animal to add to the collection, I think about what gene I don't have but I want, what I want in that gene, and if there is a combo that would fit my collection perfectly. I really want a YB female. YB spider, YB sugar, YB enchi, YB fire, YB HGW are all good options to add the gene!