For 100 visitors a day, you really don't need much of a system to host that. If you have an old desktop lying around, you could use that to start with (I'd say anything with a 1 GHz+ CPU and 256 MB of RAM should be fine for this). Just do a clean install of whatever OS you want (Linux, Windows any flavor other than 9x/ME), and then install your webserver software of choice (apache, tomcat, jboss, etc. depending on what sort of webapp, if any, you are using). Next you just need a domain name, which awhile ago could be had for $15 from yahoo for either a 3 year or a 5 year lease on the name, and preferably a fast net connection with a static IP address. Alternately you could just use any broadband connection with a dynamic address, you'd just have to kludge up something to ensure that your domain name always points to your current IP (an easy way is to get a no-ip.org account, and just set up your domain name so that it points to your no-ip address). That should be just about all you'd need to do what you want.
The advantages this has over just renting some space on someone else's server are cost (if you already have an old PC sitting around that you can use, and can get/already have a decent connection for it reasonably cheap), and also customizability, and no quotas or other limitations. The disadvantages would be that it takes more skill to set up and administer, and maybe more time as well, and if you don't have an old system lying around that you can use for it, then it probably wouldn't be cost-competitive with a hosted solution, and it's also somewhat more difficult to scale if/when demand skyrockets.