Why would you buy 1MM emails when you have no idea how to send or inbox them, lol
Cheap/Free ... umm create endless amounts of free web hosting accounts and connect them to your mailing software. In this case you'd need a bot that supported many different free hosts and could create accounts, use proxies, and crack captchas, upload a mailing script, or create email accounts via the cpanel or equivalent.
--> This could easily run several hundred to several thousand dollars.
Mailing is not necessarilly cheap or free, especially not if you need to inbox.
Your initial costs are going to be $200 - $400 range or maybe more for a good dedicated server and another $100 - $200 for good mailing software. Then depending on how white hat or black hat you plan to go you may need to look into things like proxies, domains, additional servers, and perhaps even hiring someone to train you how to do everything.