I don't have the number at hand, but the cost in feed and labor to bring a weaned heifer, (the size you get very cheap) to the point where it gives birth (and milk) is the same as what you pay for a grown one. So, even if you do it yourself you end up paying the same, just over a long period of time.
If your project is going to be as ambled without a hurry, and you want that time to build the parlour and learn animal husbandry, then I guess it is fine.
I bought several 1 year old heifers, they where expensive, because they where pure breed registered Brown Swiss, and I had to wait a more then one year to see any milk.
It seemed like an eternity since I had all the cheese equipment, bulk tank, vats and so just laying around.
Come to think of it, it did give me a chance to practice cheese making with the milk of one Old Jersey cow that I also bought very cheap (I didn't know she was 12 years old!)
If your project is business oriented, and you are investing a lot in equipment, then your accountant is going to give you a very hard time if the flow of milk takes that long!