The price is a matter only if the more expensive door has additional features as moisture-resistance, soundproofing and etc. But generally, all these things depend on the manufacturer not price. Yes, of course, there is a big gap between insulation types.

You can visit this website and find more detailed information about the advantages of steel front doors here and read about the differences between cheap and expensive front doors here. I hope these articles will answer all your questions and help you determine what kind of door you need.

The door from your home into the garage MUST be a fire rated door to slow a garage fire accessing the house. They’re generally steel. Your supplier will know local code for rating.

One leading from garage to outside is probably exposed to weather. I’d opt for fiberglass and select vinyl brick mold. Might want a half-light style for illuminating the garage too.

As to insulated, your climate will dictate and how you use the garage. We live upper Midwest and heat the garage during winter so insulated is practical.