I wear layers under a windbreaker - for a windbreaker I use a rain jacket. The layering underneath ranged from just a compression top and a T shirt to possibly an acrylic sweatshirt between the two.

To date I've ridden in temps to -25*F with that; a compression top, a sweatshirt, a T shirt over that, then a rain jacket.

At about 35*F I start wearing a neck gaiter and pull it up to cover my ears. At around 0 I put on a scarf, and switch the gaiter to a balaclava. At about -10 I switch the balaclava to a neoprene face mask.

I wouldn't buy an insulated bike jacket because I think it would only be cold enough to wear it maybe 20 days a year, when it was < 0*F out, and I can just layer up for those days.