Jars of chili oil at Jia Hua, which were going to set me back two to five bucks, had short and simple ingredient lists so I decided to make some myself. I recommend this approach for any condiment, particularly salad dressings. This way you can make and use only what you need rather than having various bought containers of salad dressings, oils, sauces, and vinegars on hand slowly passing their prime, many being kept cold by the energy of your fridge.
There are a number of recipes online for making your own flavoured oils but lots don't take precautions against clostridium botulinim, which thrive in a room temperature, moist, airless environment. Inserting a fresh herb, fruit, or vegetable in oil and keeping it on your cupboard creates perfect conditions for these pests to produce one of the worst toxins that you can ingest. So those flavoured oils and foods like chopped garlic or ginger preserved in oil can be done at home, but please be careful - make sure your recipe instructs to dry the flavouring agents completely or else uses salt, acid, or heat to retard the bacteria or destroy the toxin. (Using a lighter oil that can be refrigerated - unlike olive oil - is cheaper, safer, and also lets the flavour stand out more.)
The steps to this chili oil recipe will not result in botulism, but you could perish from the fumes. So do the toasting in a very well ventilated area, preferably outside, and do not lean over to take a whiff of the smoke just to see what I am talking about. Heat (med-high) about one third of a cup crushed dried chili peppers (I used Thai) on a dry cast iron pan, slowly, until they start to smoke and turn brown. Remove from heat, pour into a glass container, and cover with oil of choice. The oil becomes pungent within a few minutes, and continues to absorb the flavours of the chili oil as it sits. Keep covered in a dark place and use within a few months.