Well, the hosting on windows alone is not very expensive compared to linux. Pricing is actually very similar these days. SQL Server however, is quite expensive, where as MySql is open source and free. So if you host include SQL Server, then great.
You could also look at using SQL Server Express. Express is exactly the same as Enteprise, bar a few restrictions on db size and connections, etc. So if your site is not going to be massive with large amounts of traffic, that will be more than adequate. If that does not sound like it will work and you really want to save money, you must remember that ASP.NET can also use MySql. As well as postgresql. I prefer postgres to that of MySql.