Browsing through different domain servers, I would suggest a well known and established company. I would suggest the use of GoDaddy. com. I have personally used the service and can attest to their customer service available 24/7 via telephone and live chat. The provider also offers free personalized email, DNS control and status alerts for the page. The prices are competitive with other companies with assistance in not only hosting the site, they will assist in the building and maintenance of the site.
As far as domain name, at the time of searching the domain name of FreeFluShotsForElderly. org is available. I would suggest the use of a . org vs another due to the public misconception of their view towards the extensions. A normal individual may recognize a . org extension as a non-profit vs if it was a . com and not believe it to be non-profit. The name, while long, also would be easily memorable in terms of the elderly as well as being easily located with search engines as well.
Another possible alternative is to continue with a purchase like this and purchase similar domain names along the same lines and with different extensions for a cheaper price. With the purchase of the additional domain names, you can reroute users from those sites to your “trunk” site that is being maintained. Not only would this assist with individuals typing in the wrong address, it would assist with people who are looking for different sites that are mistakenly brought to this organization’s site.