Marcos,
Dont worry, your english is fine!
We dont tend to speak about the PSR8000 much nowadays its because its a rather old keyboard. It arrived in the UK in December 1997 and maybe around Feb 98 in the US (but dont quote me on that). Most discussions here are mostly of the latest keyboards, I am sure you will hear much more of the PSR9000 as it also arrives in the US soon.
I have owned the PSR8000 for over a year before I sold it, and it really was a good keyboard, but it was not my first, it was about my 14th. As for you, will this be your first keyboard purchase? If so, the PSR8000 for a very first keyboard is almost incredible. My first keyboard was a casio but I dont count that because it was really small and it had buttons for keys. My first real keyboard was the PSS780 way about in 1988 or so. The top keyboards in them days was something like the Korg M1.
Anyway, back to your question, the PSR9000 is a great improvement over the PSR8000 though thats expected because of the age difference and amount of sampled memory its got, the PSR8000 has 12meg and the PSR9000 has a staggering 32meg of ROM sampled sounds. Thats the best yet I think, though that does not mean its the best sounding keyboard (I still think the Solton Ketron X1 is and that has 24meg of ROM samples).
To finalise your request, I would say that if you can spend the money, I would go for a new keyboard as then you would not need to upgrade for a few years yet as the last 6 months nearly every single company has brought out a replacement line of keyboards. A second hand PSR8000 retails in the UK for around £900 which is around $1600 i think, but thats without any upgrades, so the price you were quoted MAY be OK but possibly still slightly overpriced. The PSR9000 retails in the UK for around £2300 which is around $3800 i think?? My personal view is that from what I have seen of the PSR9000, the PSR8000 definately resembles it, in the sense that its not totally different and some sounds are the same (sax, flutes, piano, synths), however, the biggest improvement for me were the guitars, strings and especially the drums (as it uses grooves).
The thing that really dissapointed me with the PSR9000 was that they took away the Virtual Arranger within its styles, this feature alone was one of the reasons why I bought the PSR8000 in the first place. This feature does wonders to styles (adding chord 9th to a standard chord) makes a massive difference especially within ballads. Yes the PSR9000 has 4 variations instead of 2 like the PSR8000, but I would of preferred the Virtual Arranger. Some styles on the PSR8000 I think are a little better in arrangements because of this. But thats a personal preference. Obviously the styles will sound better on the PSR9000 especially the drum kits.
So if you can afford it, get the PSR9000, if you are watching your money, get the PSR8000 as I think you would be just as content with what you getting.
Hope this helps.
Danny (UK)