Well, I suggest you first look for someone who will loan you a fast lens in that range or find one to rent and then see what you could do about the Sb-800. It's a steal at that price if it's in good shape.
Second, if the Sb800 isn't in the cards, I'd go with and Sb28 or one of the other 'super flashes' a 24, 25, 26.
I know for a fact that the Sb28 will work pretty well on my D200 in auto mode and I use often with a pc cable on a stand w/umbrella along with my Sb600. So, if you buy one you just might keep it!
If you go off brand be careful not to fry your D50 because the voltages don't alwas match up with the digitals and they are finicky so I've heard. If you go off brand, I would go with the vivatar or check the pawn shops for a sunpak 522, 544, or 555 flash. ( if you get insanely lucky and find a Metz handle flash, grab it) If you are going off brand and not getting a handle mount, think really hard about the vivitar, you don't get a rep like that for nothing.
I'm sure you are aware that you can get a hot shoe to pc adapter for around $15 and if you check strobist.com you can put together a pc cable as long as you want for around another $20 or so.
Beat of luck
mike
