There's actually quite a bit of mis-information in this thread. I know I dont have a lot of posts as I'm not quite active on this forum. But I usually post elsewhere.
If you want to post 500k worth of emails, then you have several options.
1) You get 1 VPS. You do a simple math calculation, 500k divide by 24 hours. Thats 20833 emails. Lets say you get 50 ips, thats 416 per hour. Of course, you can increase/decrease this amount but I would not shoot for more than 500 an hour. Some say yahoo is particularly harsh, in the beginning dont send more than 200 per hour. However, when you increase your reputation then you can increase this. I know someone who sends 100k campaigns just using 2 IPs ha!
2) As someone else pointed out, you can load-balance across multiple servers to not have a single point of failure. But then you need a Master server running interspire with an MTA rotator and slave servers running powermta. Servers with the right hosters shouldnt cost you that much and IPs generally run at around $1-$1.50.
3) There is no such thing as a bulletproof server. Listen, even though the VPS provider ignores complaints, the ISPs who receive the email will at some point just ban the IP anyway. Therefore even when you are sending, the ISP is just filtering it. It never even hits the spambox. So you'll just be paying major $$$ and blasting and no one gets it.