If you are in the US, be VERY carefull about loading up on high-end arrangers. There just isn't that big a market.
Probably the biggest bang for the buck is the Yamaha PSR3000 and it's soon to be announced successor. I would stick with Yamaha, Roland or Korg. Not because they are necessarily better than GEM or Ketron, but because they are more widely known and your market will be bigger.
DonM