1) There's probably not a lot of room for a res. there, but you might be able to make it fit. It'd be the cheapest and probably the easiest place to put another muffling device (2 cuts, 2 welds).
2) That'd work, too.
3) That'd work, too.

Does your ypipe have a cat? If not, that'd help quiet it down, too. Probably more expensive than adding a muffler/resonator, though.