You haven't said how you intend to use the camera. That is, will you be walking around the street, taking snapshots of the family, or in a studio. You have been given a lot of good answers already, mostly SLRs of some type or other. Nothing wrong with that.
Now if you have been around my posts long you know I am going to suggest the possibility of the Super Press 23. With a 150mm lens, it is in your price range and a good user for what you want, whether on the street or in the studio, especially if you get a focusing back for studio. Not an SLR by any means, but very useful for other types of photography too. And a rangefinder too (why would that matter here? lol).
Have you considered 4x5 if you are looking at studio? Of course, that brings in other aspects such as an enlarger or scanner that will accept that size film. But,
http://cgi.ebay.com/Calumet-4x5-Mon...569607012QQcategoryZ15247QQrdZ1QQcmdZViewItem - calumet
http://cgi.ebay.com/CALTAR-S-210MM-...573404289QQcategoryZ30076QQrdZ1QQcmdZViewItem - 210mm lens
are within your price range.
Finally, since you alredy have a Yashica, have you considered the auxillery telephoto lens for that? Especially since you want it for portraits, if there is a slight loss in resolution (and I think it would be slight), it should not matter, and will save you a lot of money.
Good luck in your choice.