Have any of you ever done work for a charity or other non-profit organization? How did you handle the financial aspect of it? Treat it like a regular commission? a reduced rate? estimate the cost and use that as a tax write-off? straight volunteer work?

It all depends on the organization. Are they an organization with secured funding or do they need to raise it through fund-raising? The former would pay more than the latter.

How much work is involved?

If it's a volunteer position (or low paying), could you complete the work without feeling resentment towards them?

It's a project for a mission through my church congregation. About 12 pages line illustration and a colored cover. I'm fine with doing it for nothing, but my mom started bugging me about it, so I'm trying to come up with a good answer to satisfy her.

Another factor I use is how much I believe in the thing. If it's for a cause you believe in, for a non-profit organisation and you have the time, doing it for free isn't unreasonable at all.

Also, anything you do gets your name out there, it can got into a portfolio etc.