For Google custom search you will need to expose all your content, I’m not sure if you want to do that. I will advice for you to look at open source, stuff like Lucerne.
Who knows later in your evolution you may want to get Intelliverb DBCSS (http://intelliverb.com/DBCSS.htm) we are currently doing a private beta for enterprise level; the hosted solution will be a perfect fit for you but that is down the line.