Coming from someone who has gone through this stage...the ring seems very important at the stage you are at, but as you travel through time your viewpoint will change a little. It is lovely to have this dream ring, but you will see other things are much more important.
Why don't you consider a different ring from Tiffanys, but still a gorgeous ring?
How about a Celebration Ring?
http://www.tiffany.com/Shopping/Category.aspx?cid=287462&mcat=148210
Choose one in your price point that will make the both of you happy and not cripple your finances. It will still sparkle like crazy and you will feel great that it is from Tiffanys as that is your dream.
Then, as a few years pass and your finances change you can either add another band and stack them or possibly purchase your solitaire you now have your eyes on.
There are no rules on how to do it. Choose what makes you happy. Some women only have one ring and some have many.
Best of Luck!
Congratulations, you have someone who loves you!!!
Oh maybe I can have a ring like this and then ad my solitaire? I wonder if it would overpower my ring? Too bad tifanny does not sell wrap..