Difficult questions - I can only help with some.
We just had our website totally upgraded and the overall cost was $1600. We were prepared to spend up to $20,000 and we had quotes of up to $17,000. The original website was created from scratch for $1100 but that was a few years ago. All we retained was some artwork of the Home page.
We are very happy with the result.
Regarding maintaining a ready built site, do you mean the uploading of new information? If so that depends on the hours you need to put in. Dont forget to factor in the cost of any upload programs you may use (Adobe for instance doesnt come cheap)
Regarding Facebook. If you create a Facebook page you will be an Administrator and once the basic information is there theres not much maintainance to do other than keeping the idiots out
You can link your sites to your Facebook page there is no charge.
Dont know about Twitter, all my friends have stopped using it in favour of Facebook.
Unless you have a lot of spare time forget the weekly newsletter its probably easier to create a link to an existing one. So many people start out with all the good intentions in the world - write one or two and then lose enthusiasm. I'm not saying you would do that but it does happen very frequently and unlless you maintain a regular schedule of new information you could lose your credibility.
Cant help with an online store - we are about to install a shopping trolley, we already have an SSL which cost us an additional $250.
Re Podcasts cant help.