Totally depends on what you want.
If you want something that just works with canned content, there are TONS of options. Just do a search on real estate website host.
If you want to roll your own, you can just get some host that supports SQL and PHP and install some content management software like Joomla, PHPNuke, PostNuke, etc. and have a decent looking site that you can put data on. I am currently experimenting with this. My current site is done with PHPNuke.
I am experimenting with Joomla (check out that effort here:
www.secureideas.com/joomla). For my first site I just went with a canned hosted one from
www.propertyminder.com. It included MLS searches, client tracking, etc. It worked great but I could not customize the look or content as much as I wanted to.
The roll your own option is actually cheaper - if you stick with all the free open source stuff. I just pay something like $13 a month for the host that keeps my site on their server. To get MLS ability on your site will cost from $30-$40 a month.
If I were you, I would start with a package site.... keep things simple till you get going.
R