Sigma makes a nice 30mm f/1.4 for around the same price as the ZD 50mm, and you can usually find it for less than $400.
Generally, with any company, be it Olympus, Canon, Nikon, etc, you are going to get what you pay for with glass. Since you are unsatisfied with legacy glass (as per your other posts), you have a few options: save up and buy a Sigma, Panleica or Olympus lens, work to perfect your technique with legacy glass, or switch brands and start asking about what cheap lenses they offer.
It seems that you are mainly looking for low light shooting, and you have a few options there as well. You could get a fast lens, but that seems to be outside of your price range. You could get a camera body with better high ISO capabilities, which will cost more than a lens, or you could get an external flash. With a flash, you can provide the light you need to work at the apertures you have available to you. You can get an FL-36 for less than $200. If you look hard on
ebay, you might land one close to $100. You could also get a legacy flash (beware trigger voltages!) like the T32. I have one, and it set me back about $20, and is a very capable flash, with some real power behind it.
I think you might get more response if you described the situations you are incapable of shooting so people can offer some solutions.