It seems Minamimoto's is the best solution. Last year I bought Rock Band 2 Special Edition (bundle with one guitar, one mic and one set of drums) for $99 on GameStop, but they don't seem to be making that deal at the moment (at least not online). On Amazon, it's $113. The Beatles instruments are prettier, so I think this set is worth the extra buck.
As for the other instruments, consider getting Lips. At $30, they come with 2 wireless microphones.
Harmonix is only selling one Rock Band 3 bundle, with the keyboard controller, so I guess you don't have much of a choice there. And it's sold out at Amazon, which is even worse.
As for the cymbals, both RB2 cymbals and the new Pro Cymbals are being sold by the same price, $40. The only issue is that the new Cymbals will only be released on October 30th. According to a review, the new cymbals are much superior, so it might be worth the wait.
The only thing missing is the guitar. There are several options. You could pick a RB2 Wireless Guitar for $60, not much to go wrong there. With $20 more, you could get the Beatles Guitar, which could be nice if you get the rest of the set. If you prefer the Guitar Hero controller, it would be the cheapest option, at $50. And, for $70, you can get the Guitar Hero: Warriors of Rock guitar bundle.
You'll be spending at least $360 on all this stuff. But your parties are never gonna be the same. :-)
EDIT: Ah, and if you want to crank it up to eleven, get this setup.
Best Answer
First make sure "Sorted By" is set to "Song Difficulty." Next, You also need to set "Instrument Scores" to "Pro Keys." I tested this by setting Instrument Score to Keys, and it sorted by difficulty with normal keys. I then switched Instrument Scores to Pro Keys and it sorted by Pro Keys.
I tested this on the 360 version.