Pricing for a freelance client-a credit union.

So I was contacted by my credit union to do some freelance work for them. After meeting with them it looks like they would have work to keep me busy for at least a few months (right now I also work full-time temp designer at my day job).

The Marketing director saw my business card on a table downtown at a local shop, she picked up, looked me up, liked my work and it just kind of stuck in the back of her mind (as she describes it). Originally we had a phone call in February about doing some redesign/refresh of their business materials with their newest logo/brand identity that they had just got. A few weeks ago they reached out again and wanted to meet and get things started. I met with the marketing director on Friday and they have several projects that they would want me to do ranging from brochures to volunteer shirts.

Right now the two bundles that I would tackle are the volunteer shirts and their the letterhead/business card/envelope.

I was thinking about charging hourly ($15-20) for the shirt design, and a flat fee for the letterhead/businesscard/envelope. I live in the US/Midwest/West Michigan area. I have no idea what a decent flat rate would be.

I told her that I would look at the work, and come up with an estimate for those things over the weekend while I get the contract sorted out. Then she started stressing to me that they want to work with me, but they also want to be ethical with how they use their members money and gave an example about how they spent big bucks for marketing research/logo rebrand and basically got their same look thrown back at them and were unhappy with it. I really want the project, as we're pretty slow at work so we keep getting let out early. Any pricing advice would be appreciated!

Here is my website if it helps:
http://www.traceyhowell.com/