that seems reasonable for a hobbyist if you are fast enough. The best way to decide would obviously be to know how loong it takes you to get a comic page done, remember that when you are doing something for someone else they will probably want you to make adjustments and changes to it, which will also just add to the time. I find it strange that someone would commission you for a comic page when I don't see any comic pages in your gallery though. :/ . Comic pages are much harder to do than single pin up style drawings and require much more thought.
It depends on what they are willing to pay and how bad you want the job. I usually try to think how long it's going to take and base a price from there. It say it would take me at least 8 hrs to do a page from layout to inking. So a $100 a page is going to be maybe $10 an hour.
Raerae is right there is a lot more setting up to doing a story than a single drawing.
It totally depends on you. From a business standpoint I'd like to think that I'm skilled labor and worth at least $10 an hour. Reality is how much money can they spend or how bad do i want the job. I use to do free art for San Diego Con for years just because they USED IT and Printed It. It was worth being seen to not get paid for it.
Possibly. Do take into consideration that there's a lot more to drawing comics than just characters, though. There's also panelling, pacing, and the fact that you're telling a story. Honestly even at your price range, I wouldn't do it for less than $50/page.