I'm in the market for an ASP.NET host to start learning on and to host personal projects. I've noticed most of them provided both MySQL and MS SQL databases. However, usually they will only provided a couple MS SQL databases, but a large number (like 10) MySQL Databases.
Can I use a MySQL database as a back end to a ASP.NET website? If so why would I want to pay extra to use MS SQL over MySQL?
If you're more comfortable with Sql Server then clearly it'd be worth going down that route, for a small scale site it really does come down to personal preference. That said there are things such as the asp.net membership providers that come, by default, with support for Sql Server as opposed to MySql so that could be a deciding factor for you.
Ultimately, it comes down to personal choice. Which do you prefer and are you willing to pay if Sql Server is your preference?
Yes you can use MySQL to drive a website using ASP.NET or any other web development technology for that matter. The reason for choosing SQL Server over MySQL would if there were features or performance characteristics you wanted in SQL Server that did not exist in MySQL. For example, common-table expressions do not exist in MySQL. If there are no features in either that are driving your decision, then it comes down to personal preference and cost.
This article is a detailed comparison between MySQL and MS SQL. Maybe it helps making a decision.