Getting married! your thoughts please. 8)?

Hello, I am 23 and my girlfriend is 25, weve known eachother for years as friends, and weve been together as a couple for a few years now. We've been through alot together, and we lovingly share our life, thoughts, feelings and everything you could ever want. We both share dreams of getting far in education wise, and we are working hard at it. We've discussed our future in great depth, and plans for our future. We plan to have children and raise a family together. We've talked about marriage before and i think thats the next step. The relationship we have is honestly the greatest thing to happen to me, from day one shes made me the happiest ive been, she is always there for me, to support me through lifes decisions and to better myself for myself. I dont have very much money at the moment, I have about $2000 to my name, and of course i am working and studying hard, but I was wondering what you guys think I should do. I truely feel that I am physically, and mentally as ready as I can be to ask for her hand in marriage. Her family knows that we are going to be together, because they have never seen either of us as happy as we are with eachother and they have no doubts of us.. Do you think I should invest in a engagement ring soon? even if i dont tons of money layng around, only about $2000.. please help.. and also how much is a good price to invest in a ring?