As an MLB fan and current Dish Network subscriber, I'm looking for an alternative to be able to receive the MLB Extra Innings package. I currently subscribe to the lowest tier of Comcast Basic Cable along with my internet service, since the price is only a couple dollars different than internet alone. Would there be any way for me to subscribe to Extra Innings along with this package, or would I need to upgrade to the Digital Starter pack?

You have to have digital cable to get any of the sports packages.

You have to have digital cable to get any of the sports packages.
Are the sports packages available with a CableCard in place of a Set top box? Also, if I were to upgrade to the Digital Starter package with a CableCard, would I automatically get HD channels or would I have to spend the additional $8.99/month? It's not clear to me whether the $8.99 fee is for channel access or the HD box.

The $8.99 gets you access to the HD channels you'd get with whatever HD package you choose.....the cablecard will afaik get you the sports packages but check with the local office just to be sure.