I'm going to say something that will shock people here on the kindleboards
If you can write the book that quickly, the proposal is easy AFTER the fact (if you do it, DM me and I'll find the two books I found most helpful) -- AND if it's a topic that will get you a large enough advance to help you support your other writing AND a publisher that has national exposure pull.... the worst thing that happens is you say "no" if they don't offer you those two things, the book is done and you publish it.
There have been several authors I've met who have said on the DL after doing something like that, they later wrote the agent a one time "consultant's fee" check the agent wasn't expecting after their self-pub started bringing in real money.
Lots to think about. Either way, you're on a path to success, right?