to get the full benefit of developing in ASP.net your going to want to get copies of visual studio pro and SQL server. If you are a student you can get these free:https://www.dreamspark.com/default.aspx
if your not a student you can get free express editions which do work really well.
you can use MySQL with asp.net and you can user other tools like dreamweaver but why??
Hosting a live site on ASP.net tends to be more expensive. Especially if you are not running mission criticle things. If you are just running a personal site you can get cheap hosting from places like Dreamhost but at that point you want to be running PHP and MySQL.
Php is a really easy language to learn and you will be up an running in know time. You will find much support on the web as well as free scripts to get you started.
The other thing that can be difficult for beginners to deal with is the backside of an ASP.net site. You are going to have to be programming in either C# or VB.net and that means managed code, meaning it is compiled.
PHP is not complied. so sometimes it can be easier to track down bugs and broken code.
You can download everything you need to get started on PHP for free if you are runnign on windows I would download xampp: http://www.apachefriends.org/en/xampp-windows.html
and eclipse with PHP
http://www.eclipse.org/pdt/
good luck
