GOTY adds all 5 expansions for "free" while they're a total of $50, or $10 each, if downloaded separately for the regular version. It should be noted that the GOTY is extremely glitchy and you may tear your hair out.
Personally, I stuck with regular Fallout 3 and just downloaded the Broken Steel add-on which raised the level cap to 30, rather than dealing with the horror stories I've seen in reviews of GOTY.