I don't believe you will be able to find reliable 7mbps (that's megabits, not megabytes, which would be rated as 56 mbps) over a wireless broad band card for your office. I would give DSL Extreme a call - they are a DSL provider in CA and may or may not provide non-profit discounts. You should be able to get what you're looking for at less than $100 a month. I'm not sure what you mean by low-price.
For landline, is there something wrong with your telephone company? If you have reliable Internet you could try what we do for my company. I purchased the $49.95 / mo plan from grasshopper.com that got me 2000 minutes, a local number, a toll-free number, and 20 extensions. The extensions are virtual, and if you want them to ring a phone you have to provide them with the number (say your cell phone or a Skype-In line which are $30-$50 / yr). Best of luck!