There are still some good quality instruments available at affordable prices. I think Martin guitars are among the best quality you can get and here is a great example of a really beautiful guitar that isn't overpriced - Martin D15 Acoustic Guitar
I really was referring to keyboards not guitars and basses
but since you bring it up.
guitars are coming down
at least the big names like prs washburn etc
have introduced inexpensive versions for the everyman or everywoman to play
but keyboards have not really done this well
sure the big names have introduced cheaper versions
and they really are cheaper in every sense of the word..
I bought a prs for 500 I am sure it is not the same quality as the 3000 dollar prs
but it sounds pretty good plays really well
and when it comes to guitars it is all about the hands
I am sure if I wanted to upgrade a notch or two I could change the pick ups and I would be good
the best sounding guitar I ever heard was mexican tele with a seth lover humbucker in the neck position and a dimarzio split rail in the bridge
the guitar probably cost around 400 dollars and add about 300 for picks ups
but keyboards are not like that
keyboards are computers and unless you can significantly upgrade the memory or motherboard
you are stuck with what you have
the only upgrading you can do in terms of sound quality is to buy a brain