chances are my friends wont buy into this game, so my question is simple. What is the easiest and best and cheapest way to buy a big enough set for several people to play?

Buy the core Set, contains 4 pre-built decks that are fairly balanced (giving the decks out based on experience level helps some strategies require a more experienced hand, least to most, Orc, Dwarf, Chaos, Empire), and if you want people to enjoy the thrill of customization grab some of the Battle Packs out. If you have a group of larger than four you may want to buy the Assault on Ulthuah Delux Expansion which introduces the High and Dark Elves, or an additional Core Set.

As to where to purchase it, I always recommend checking with your Friendly Local Game Store (FLGS). Brick and Mortar stores often times will know of other players who frequent their stores who play the same games as you and give you a chance to grow your play group or play outside of it. Not to mention the extra money you would save on by purchasing it online really helps a local small business stay in business. If you have no FLGS, then you can buy it direct from FFG I believe, if not try coolstuffinc.com.

I'm not completely agree with master Dormouse

It's true that there are four 40 card decks in one Core Set, but the number of Neutral cards will be lacking for 4 people. (There is 24 per core set)

I recommend 1 set for 2 people and 2 core set for a maximum 4-5 player. That also gives you the possibility to play Ork vs. Ork and similar matches, as you will have 2 Capital cards each.

If you want to play with your frinds al toghether at the same time, by 2 core sets.-

And 1 of each BP.

After if you want more by them.-

Juan