How to make a website? Is it expensive?

[Pixie]

I want to make a dating/social media network for people like my parents. My mother contracted herpes when my Dad cheated on her a month ago and she's finding it really hard to find someone to date. I want to make a site solely for people who were unlucky enough to get this disease(and other diseases that can't be cuted) whether they were born with it, got it from someone they loved and thought loved them and everything else in between. I want this to be a safe haven for people with this common factor in their life.

I'm not sure if there are other sites for people like her but I want to make one that is very... modern. I want it to be a blend of CafeMom and Facebook.

Here are the features that I want:
>I want the users to be able to make groups and post... well... posts in this group that others can comment on and that only group members can see. (This is a feature on CafeMom that I really enjoy)
>I want people to be able to make a profile (Like the ones on Facebook) with their bios, what they're looking for, pictures, location and whatever else they feel they need to post.
>They should be able to make their pages private and customize it to describe their personality and style.

These are the main features I want for the site.

How much does this cost? How do I make it?
I would advertise it with pamphlets left at clinics and support groups. But how do I advertise it online?

I reeeeeally want to make this website look... Modern. I don't want it to look like some cheap forum or anything because that isn't what it is. It's a social media network that should be used to find similar friends, people to date, support groups and... well.. Help. Because everyone deserves a place where they can feel safe and not judged.

PLEASE NO BASHING COMMENTS!! I really want to make this happen.