This is a wide topic and can drastically vary depending on your market. Various methods include;
3x material costs
2x material cost & time it takes
Stitch count
There is no right or wrong way, there are also tons calculators out there that you enter material cost and a desired hourly wage and it puts it all together.
Sometimes its just asking others what they have been able to get for their products.
So as a community lets utilize this category to help with pricing and share any tech that you may find useful in your crochet life.