For weighted keys, you'll be going with an 88-key model most of the time. In the keyboard world, there really isn't much that's got a large number of great quality sounds but limited features, and you're always free to ignore what you don't need.
If you don't want to pay for a Fantom, though, you're probably not going to be able to get anything cheaper without sacrificing quality. You've got some possibilities though.
1) Spend a few hundred on a good MIDI controller and buy a rack module to go with it. For the best sounds, you'd be looking at the Korg M3-M or something in the Yamaha Motif line (Motif, Motif ES, and Motif XS all have rack versions). Korg is probably the better choice if you want access to more electronic sounds, and Yamaha is probably the better choice for more acoustic sounds, but try them yourself first, if possible: people here disagree on which is better in which case, and you know best what sounds you want.
If you're going in-store, just try out a normal Korg M3 and Motif XS; if you're going rackmount, the feel of the keyboard doesn't matter (the ES and regular Motif are discontinued now, although it's not hard to find one second-hand). The Motif ES also has the same sounds and engine as the MO6 and MO8.
As for controllers, I don't know anyone who makes fully weighted controllers besides M-Audio. They have two options: the KeyStation Pro 88, which is strictly a controller, and the ProKeys 88, which is a stage piano (can act as a controller and has a small number of sounds).
2) Get a previous-generation workstation, if you can find one: Korg TR-88 or Triton Extreme 88, used Fantom-X, Motif ES or Motif. You'll be hard-pressed to get good piano sound out of the Triton Extreme or TR-88 though; even trying out patches that other people have made and posted online, I wasn't impressed. You could get a keyboard with sampling and find/make your own piano samples to get better sound, if you wanted. The TR-88 has a sampling upgrade, and I'm pretty sure everything else I just listed has sampling. That might be more work than you'd want though. Still, you could try out some older keyboards if you have the chance, and see what works.
3) Nord Stage/Stage EX or Nord Electro 3. The Stage series would give you great piano, B3/Vox/Farfisa organs, rhodes, and wurlitzer sounds, plus a synth module you could use to add some synthesized strings or other sounds. It's a great keyboard (I use one and love it!) and while it wouldn't be my choice for exposed strings, it's good for layering synth strings with another pad plus piano and other stuff.
The Electro 3 has the same piano and organ engine, only you can only use one at a time, and it also has a sample engine that lets you load samples provided by Nord (loads of Mellotron stuff, plus a reasonable cross-section of other sounds, including brass and strings) or roll your own from WAV files using the sample editor software. You'd get more realistic strings here, but unlike the Nord, you can't play as many instruments at once. I'm not sure how they've done it exactly,but the previous Electro could only play one of either piano or organ at once (it didn't have sampling), so it's possible you'll only be able to play piano or other samples or organ here. It's a very new release and the website doesn't say. Being limited to one instrument at a time could be a problem, but this may not be the case.
4) You might also want to consider Kurzweil. They've got some stage piano-class keyboards that are possibly cheaper than the Fantom and definitely simpler, but still have some great sounds. I've never played one, but listening to demos online, even their lower-end stuff, says that they've got great-quality sounds. My impression is that spending roughly the same amount of money on a Kurzweil compared to the big 3 (Korg, yamaha, Roland) will get you less features but better sounds, but I could be wrong here.
Anyway, I've at least given you lots to think about
