I have been following the prices of the Power 9 online, and, finally, they have gone down enough for me to complete the Moxen. I am not sure if and when I will get the remaining cards. I still do not have any Force of Will. I do have a playset of Jace, the Mind Sculptor. My current selection is good enough for casual Vintage play, and since I only intend to build decks for solitaire, I have what I need. The number of people who play Vintage online is close to zero, and the ones who do, like to play with full Power.
Sometime back I net decked the Vintage competitive shell.
Here is my casual Vintage shell. It's 26 non-creature spells and 2 lands. That leaves 32 other cards, including some lands. The Moxen act as lands. You are only going to need to run something like 15 lands. That means that there are 17 free non-land slots.
March 19, 2017 update: Ancestral Recall for $19 from the bots.
August 19, 2017. Ancestral Recall is a little over $10 today... oh, well. $17 to the bots and now I am only missing Black Lotus.
August 20, 2017 Update: These are the cards that I am missing for Vintage and Legacy play. There are additional cards for specific decks, but these are must-haves for the majority of decks. I don't even have enough money right now to buy all of these cards, and that means that I will only be getting them when they get reissued online. I got Flusterstorm (had one, got two), Hurkyl's Recall (had none, got two), and Mana Drain (had one, got three).
August 22, 2017: Even if Black Lotus goes down in rent cost (not really value), I want to play it soon. $45.77.