Advise on Authenticode Code Signing

I've been deploying my apps and installation packages signed with a Thawte certificate for many years. No problems. It's due for renewal again and I was looking round for alternatives. Thawte is around $300 for 1 year. Comodo is around $80 for 1 year.

Does anyone have any comments about why there should be such a BIG difference in price ?

Can I invite discussion on authenticode certificates in general ? What do you guys use ?

Thanks
Ian