Hello,
I have quite experience with SOAP integration projects, especially on Microsoft Windows platforms. So, if you consider to use IIS, I could be a choice. I'm proposing a WCF webservice, built with VS2012.
You didnt specify the authentication mechanism you want: usernames and passwords from database, as embedded "resources" just for demo ? You want the authentication to be made by using the header of the SOAP message, or could be tags inside the SOAP message ? ...
My estimate of 2 working days assumes that the messages exchanged have only a few tags and we are not talking about cascaded methods - if the SOAP exchange is more complex than that, an extra day could be a posibility.