Is JQGrid free?
There are two versions of jqGrid: Free, Open Source package as pure JavaScript solution delivered with GPL & MIT licenses and commercial which is integrated in for example Visual Studio development environment. You can use any from the versions in your ASP.NET MVC Project.
jqGrid can be used to fill data from almost any web service providing data in JSON or XML format. So you can write in ASP.NET MVC a Controller method which provide pure data in the JSON format and use View with empty <table> having only an id attribute defined. If you want you can implement the "data provider" as ASMX or WCF service. You can also combine any from the solutions in one site, so you will be free in the implementation.
Look at the other question where you can find some links with examples of the usage of jqGrid with ASP.NET MVC.
UPDATE: The answer is old and the licence agreement is changed now. The there exist two main forks of jqGrid: 1) free jqGrid, the fork, which I develop since the end of 2014 and which I provide under the old MIT/GPLv2 licence; 2) Guriddo jqGrid JS, available for the prices. You can read more detailed about the problem in the following more recent answers: this one, this one and this one.
Not anymore!
"jqGrid JavaScript shall change its license from MIT/GPL 2 to Creative Commons Attribution-NonCommercial 3.0 License. This means that the code can be seen by everyone but in order to use it commercially, the relevant license has to be paid."
From http://www.trirand.com/jqgridwiki/doku.php
"Tony developed jqGrid and made it available for free as a way of making a contribution to the open-source community.In addition to the free jqGrid, Trirand also develops commercially-available, server-side grid components for PHP and ASP.NET. These components are not required for jqGrid to work, but they speed up the process of making complete grid solutions, and they save developers the effort of writing server-side code. "
So, yes, it's free.