The price is dropping because the new 50mm 1.4 II (probably with IS) will be announced. I'd rather be patient to see the price point on the newer lens (which will be high).
On crop sensors, 50mm is too long. Get the 30mm for a general walk-around. For portraits, get the 50mm.
And whether to get the 50mm 1.4 vs 1.8, well I would definitely say 1.8 for performance/price. One hardly ever shoots at anything below 2.8 and at that aperture, both lenses are identical. Even at 2.0, they are pretty much the same (the 1.4 is slightly better). If you think you'll need 1.6 (cause thats the only f stop available that the 1.8 doesn't have, because using 1.4 is impossible, the lens is too soft), then get the 1.4. But, you will more than likely be using 2.8 on either lens, which makes the 1.4 pointless. If you need to stop down, go to 2.0, but thats more than enough DOF on a crop with this 80mm equivalent.
Think about it:
-you probably need a DOF of 1ft to get a face all in focus (forget group shots, just a portrait)
-using a 50mm on a crop at 2.8 standing 7 feet away from your subject, yields a DOF of 0.63 feet
-using a 50mm on a crop at 1.4 standing 7 feet away from your subject, yields a DOF of 0.31 feet
-you either need to step further away to get more of your subjects face in focus and crop in post, or increase the DOF by using a smaller aperture
-at this distance, you will more than likely use 4.0 and above, rendering the 1.4 useless
-and, if I were to use 1.6 and want a depth of field of 1.05 feet, I would need to stand 12 feet away from my subject. Ask yourself, how often do you do that? Is that even possible in doors? How would the shot look when the persons face is so small etc.
In the real world, there are very limited situations you can actually use 1.4 or 1.6. For a lens that costs 3X the price, definitely not worth it. Where 1.4 would shine is on a wide angle lens when you want a lot of background in your composition, but a very narrow DOF, like a model in a field. You want the field, but you want a razor thin DOF to get only her in focus with the rest blurred out. Thats why if you are looking for a 30mm 1.4, the new Sigma Art coming out this week will be fantastic.
I have no idea what I'm doing.