Need access to SQL server (I think)
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I am developing an app that calls for Windows, Mac, Linux, iOS, and Android devices to access a server to upload and download data.  The data will need to contain the user's username, and 40+ strings each containing web addresses up to 200 chars long.  I think what I need is an SQL server, but I'm not quite sure (I've done almost no work in the remote context, mostly local).  And also I'm pretty sure that AJAX is involved.

So, what do I need, how do I get it, and how much should it cost (if it would cost anything at all)?