I went with the dig it myself method and used a pond liner. I dug it much deeper than needed for now, and then filled up with rocks to bring the bottom up. I'm also switching to this filter (non-pressure based so you can open and clean while it is running, and have to clean less often - a little more expensive but with my current filter, I was having to clean too often - if you have time and don't mind there are some cheaper options):
https://www.amazon.com/dp/B003JVR1VS/?tag=exoticpetnetw-20
I just connected a standard pond pump, and also got a pond pump barrier bag which does a good job keeping the big stuff out.
I added some water lettuce, 10 small minnows and a pleco to help keep it cleanish (and to eat the mosquito larvae)
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