DVD-Audio uses the higher storage capacity of a DVD disk to hold uncompressed audio information that yields a greater dynamic range and frequency response of conventional CDs. Long story short, they sound better than CDs.
SACD also should sound better than CDs.
The problem is that most people don't have any complaints about CDs, so you can't get them to buy into these formats based on sound quality alone. Both formats also offer multi-channel operation, so that might get people interested.
The problem is that like the early days of stereo, many sound engineers aren't quite sure how to handle this new toy, so you'll be seeing a lot of "ping-pong" effects, and the audio purists will say that's proof that it's a bad format. Well, they said the same thing about stereo too, when it was full of "left-right" effects.
There's alot of other factors involved, both technologically and politically, but I'm not about to get into those here. A subscription to a decent audio magazine or a thourough reading of this forum can help you out a lot with that.
If you get a player with DVD-Audio, there will be a decoder for it in the player, and you'll be able to take advantage of it using the 5.1 channel output. You may or may not be able to take FULL advantage, based on the features of the player. In your particular situation, I wouldn't say that DVD-Audio is an absolute necessity. There's not a ton of releases, and most of what is actually released is stuff that you wouldn't be interested in.
Get the cheaper player. When the dust settles in the "format war" you can think about what kind of player to get then.
Mike