I have less information about share point (only basic info). Microsoft released SharePoint for web developers. Microsoft also said SharePoint has compatibility with other .NET t
SharePoint is an Application that sits on top of ASP.net (3.5 SP1 in the current SharePoint 2010 - No ASP.net 4.0 will be possible). They do override a lot of ASP.net built-in functionality (they have their own .aspx Parser and Virtual Path Provider for example).
With ASP.net you have a very well documented, battle-hardened, mature and stable platform with a good API.
With SharePoint you gain a poorly documented, bug-ridden, very limited application that handles a lot of features that you would have to code yourself (e.g., User Profile Management, Document Organization and Versioning and Social Features like Commenting and Tagging), although for the most point SharePoint handles them really poorly and does not allow you to override them, which means that you spend a lot of time rewriting them anyway and trying to integrate them back.
Basically my advice as a SharePoint developer since 2006: Use it when you absolutely have to, avoid it whenever you can and stay with just ASP.net.
SharePoint is good as a simple document management and very light social system. You can quickly customize smaller parts of it and add a lot of value to your company. But in the moment you need something that even only slightly different from what Microsoft envisions, you hit a wall that you can't pass. It's great for what it does, nothing more, nothing less.
SP is a very powerful platform, however, it does seem to bring complexities to the table that otherwise may not be there with simple ASP.net. Plus when you move "OOTB" with SP it becomes a bit challenging with RTM, etc. I live in blogs with "weird" things that happen. I am not a full blown SP developer but have been working with it for over 7 years and well, I find building solutions that will work within SP, but not necessarily built withIN SP generally are going to be easier to maintain and controllable. Just my opinion!
I'll try to answer point by point:
I would compare all for you and its up to you to decide.
Say now you need some more PC for your servers and so your costs go up all the time you need a new server
If you just want to create a website, go for ASP.net.
However, if your company has a SharePoint installation and you want to integrate with that, you should go for SharePoint.
SharePoint is build on ASP.net, but has many extensions that allow data to be shared throughout the company.
However, if you are just building a website and don't need all that, ASP.net is the way to go.
Don't use sharepoint unless you need it, check this article: Challenges when using SharePoint compared to ASP.NET