An endcap that fits left side of common vinyl gutters available from big box hardware stores in my market. The specific model I am using this with is Amerimax 5" K Style gutter. When two pieces of plastic endcaps in the shop are $10, and the whole damn gutter only costs $8, you can see clearly all the profit margin gets jammed into gouging on the accessories. Combine this with Sawncraft's hangers (https://www.thingiverse.com/thing:4354310) and you can hang some basic cheap gutters for reasonable materials cost.

I will eventually figure a downspout adapter maybe, where I'm hanging I just need to route the water out one end of the gutter and it will land on concrete that it won't erode even without a proper downspout.