Well, an 06 325i is going to be hard to find (the one that you want). Since you cannot order a 325i anymore (328i and 335i are replacing them). I would reccomend Devon Hill, West German, Otto's. All those are good, i'm currently dealing with Devon Hill at the moment, and they're service is great!
About $500 invoice, they're not giving the 325i's for free now haha. Dealers still have to make profits.