Hmm. Most synthesizers have decent electric-piano tones, and cheesy '60s transistor organs like the Vox are also common, so you should be good on those fronts with just about anything. Really good acoustic-piano sounds are less common, but if you just want it for practice maybe it's not so big a deal?
You might try a Yamaha TX81Z - it's got ROM presets for a couple of excellent Vox-type sounds ("6 Tease" and "Farcheeza") and some good Rhodes/Wurlitzer tones, and a few acoustic pianos that are decent by FM standards (though that's not saying a lot,) along with a bunch of other sounds in various categories and user-programmable slots so's you can experiment with FM synthesis or dig through libraries of a few thousand patches (do yourself a favor and use one of the available computer programs for this, though - the onboard menus aren't particularly intuitive!) And since it's purely algorithmic synthesis, the voices don't fall apart outside their nominal range as badly as they do on a lot of cheap PCM ROMplers. You can get one for around $80-100 if you keep an eye out on eBay.
If you can spring for something more in the $150-200 range, you could dig up a Korg 05/RW or the upgraded X5DR. I have an 05/RW I've been very impressed by; I don't usually go in for ROMplers, but I fell in love with it after hearing some demos and had to get one. It's got a very broad, non-generic and creative palette of sounds and a good bit of potential for creating new ones using the ROM samples, which are surprisingly good for something of its vintage. (You can even get some Mellotron-type sounds out of it with a little work!)
If you just want something cheap, the Roland MT-32 is a bit of a classic in gamer/computer circles. It sounds pretty cheesy, but you can get one for $30-50, which is dirt-cheap for a hardware synth, and it's possible to create significantly better sounds than the presets. The big downsides are that it tends to be noisy, it has no onboard editor (which means you'll need a computer program to roll your own patches,) and - without modification - it doesn't store user tones or settings when powered off (which means you'll always need to load your custom patches in from the computer.) It's cheap and has potential, and you can listen to some cool old music from various Amiga/PC games that supported it, but I definitely wouldn't recommend it if you plan on doing any live performances.
You might try a Yamaha TX81Z - it's got ROM presets for a couple of excellent Vox-type sounds ("6 Tease" and "Farcheeza") and some good Rhodes/Wurlitzer tones, and a few acoustic pianos that are decent by FM standards (though that's not saying a lot,) along with a bunch of other sounds in various categories and user-programmable slots so's you can experiment with FM synthesis or dig through libraries of a few thousand patches (do yourself a favor and use one of the available computer programs for this, though - the onboard menus aren't particularly intuitive!) And since it's purely algorithmic synthesis, the voices don't fall apart outside their nominal range as badly as they do on a lot of cheap PCM ROMplers. You can get one for around $80-100 if you keep an eye out on eBay.
If you can spring for something more in the $150-200 range, you could dig up a Korg 05/RW or the upgraded X5DR. I have an 05/RW I've been very impressed by; I don't usually go in for ROMplers, but I fell in love with it after hearing some demos and had to get one. It's got a very broad, non-generic and creative palette of sounds and a good bit of potential for creating new ones using the ROM samples, which are surprisingly good for something of its vintage. (You can even get some Mellotron-type sounds out of it with a little work!)
If you just want something cheap, the Roland MT-32 is a bit of a classic in gamer/computer circles. It sounds pretty cheesy, but you can get one for $30-50, which is dirt-cheap for a hardware synth, and it's possible to create significantly better sounds than the presets. The big downsides are that it tends to be noisy, it has no onboard editor (which means you'll need a computer program to roll your own patches,) and - without modification - it doesn't store user tones or settings when powered off (which means you'll always need to load your custom patches in from the computer.) It's cheap and has potential, and you can listen to some cool old music from various Amiga/PC games that supported it, but I definitely wouldn't recommend it if you plan on doing any live performances.