craftgrrl | magnet prices/tack sizes

i'm pretty sure this hasnt been asked before, so i shall ask it. i went to wal-mart and lewsicraft and both places the round thick magnets cost two or three dollars for a pack of four/six. i was planning on making 50-ish.
i got a pack of marbles which work great from a dollar store, so now i just need to find cheap magnets because theres no way i can afford those.

1) can you get them cheaper from anywhere else or should i just make marble tacks instead?
2) where can you get tacks that are big enough to fit the back of the marbles? i used a regular sized one for this and its a bit smaller.

thanks in advance ^_^

"this" is my first ever marble tack. yay. it actually says you? but the light is hiding the question mark.