Keep in mind that you can kind of control your costs with materials, tools and parts, so once you know what you need, you can get it done. I’ve seen lathes costs under $500, but are they good enough? That I cannot answer, but I will say it was being sold by a place that specializes in skill toys and yoyos, so that might be an indicator that “hey, maybe you should use this to make yoyos”. I’m not sure if you can use these lathes to turn metal into yoyos. Again, I have no idea. I buy yoyos, I play with yoyos, I don’t make them. I don’t want to, I don’t want to learn how to either!
What you can’t factor in is the time and effort it takes to learn the skills you need to turn your own yoyo.
I suppose if you can figure out a way to make those sand-type molds and then die-cast them, it might drive costs down, but I hear there are other issues that can come from this method. You still have to come up with the master item to base the molds on and know how much the metal shrinks when cools. or maybe you can make plaster molds?