If you are willing to wait on delivery and take somewhat of a chance, there are really cheap down pants on AliExpress. I suspect the fabric is thin so they must be worn either indoors or under a shell.
I purchased down mittens on AliExpress for my wife that appear to be made of the same fabric. They are puffy and light and seem fine, but should be worn under a shell if you are handling anything.
Note: be careful on sizing, read the charts carefully. I’ve had to purchase XXXL on occasion, and I’m not that big!
Otherwise I’ve been generally happy with purchases on AliExpress (some outdoor items, a lot of misc stuff, including clock/watch repair tools). A few never arrived and I got full refunds. I routinely see identical stuff selling in the US for way more.