I make a lot of my own popcorn on the stovetop, for chili powder I just mix X amount into the popcorn seasoning jar & mix it good before shaking on the popcorn into plastic food container. The best way to infused flavors to the popcorn is the toxic way you know about - mix seasonings in the oil for 1-2 days to blend well & use it all up too. Or you can just add more oil for popping to have it more moist so the mixed chili seasoning stick better.
The seasoning infused oil method I do for Dill, dried Dill in oil (just what I'm going to use) intense dill flavor with dill Kernel Seasonings.
I save that flavor for last since it makes a big mess in the pot, & don't blend flavors. Any other type of liquid seasonings I've found makes cleaning more work gets caked/burnt on the pot.
I'll make 40 quarts of popcorn at a time ( I said I make a lot ! ) 3-5 different flavors at a time. Here's some other info you can use if want.
If you like Kernel Seasonings seasons, for price best is Walmart & Menards - same price but if Menards offer a discount / rebate even cheaper still.
When it comes to popcorn kernels & oil, Snappy popcorn is the best price for both !
snappypopcorn.com
I don't know your method of making popcorn but I love my Zippy's stainless steel stovetop popcorn maker, they're kind of difficult to find.
Then a 8 quart container holds 3 pots each, & perfect for shaking the seasonings onto the popcorn with a good seal to keep it fresher longer.