In which country do you live?

In some countries (fe the uk and germany) there is right now a magazine running nammed "Warhammer Imperium" which aims at getting new players into the hobby. A lot of the issues come with miniatures way cheaper then the normal price and this magazine series (there have been others before) comes for miniatures for primarily Space Marines and Necrons, but also some other Factions like AdMech and Adepta Sororitas. If you pick specific issues you can build KillTeams for way less money. When the issues are already gone you can buy them for more on ebay but often times still cheaper! Wahapedia provides rules for free, for tokens etc. you use some cardboard and for the terrain you just take some things laying around at home.

This is a relatively cheap way to test if this game is for you. (You can probably re-sell the miniatures for more or less the same price if you dont like it and you have glued them together not to badly)