If you hve to chose one, unless you are doing a significant amount of metal work, my opinion is that the drill press will get much more use and be helpfull in your modeling. I would get a disc sander before I would get a bench grinder (I have one and use it a great deal). I do not have a bench grinder but so far have not felt like the lack of one has hindered my building. Once or twice in the past 10 years I have needed the use of one and have been able to pop over to a friend's house.
Lars