

A cheap solution is to wax some thrift store or old trousers. Beeswax and paraffin, there are different ratios to experiment with, and premade bars you can buy. You rub some on and heat with a hair dryer or clothes iron (with parchment paper so the iron doesn’t get wax on it). It’ll darken the cloth. The more you put on the more waterproof and wind-resistant it’ll get. For bike pants you could focus on the front of the upper thigh and coat the rest less, leaving some breathability on the back.
Yes, it’s used to make oilcloth but as far as I know, you’d have to leave the garment to dry somewhere with ventilation for a week or more. However I’ve not done it so if that isn’t the case please correct me.