This is not intended to be a typical "equipment recommendation" question. The answer should be moderately stable and potentially useful to others.
To meet a one off need I want to buy a minimum cost external flash compatible with Nikon D700 that works in sensible "auto" mode (ie not a full manual flash but need not have many bells and whistles). My significant experience with Minolta / Sony flashes indicates that having significant experience with brand specific flashes is a good idea. I don't have such experience with Nikon.
Budget: As little as possible. As much as necessary.
A degree of manual adjustment is acceptable if essential. I'd like to avoid a fully manual flash such as eg the low cost Chinese Yongnuo 460 and similar (about $US70 new here) but even that would (probably) be suitable.
I will seldom need or use a flash with the D700 so would like to know what works acceptably as an entry level flash. It may well be that there are workhorse secondhand Nikon flashes - maybe film era ones - that are cheap and common that will meet the need. Minimal guide number is required - the on-camera flash is bright enough but I'd like to be able to move the flash off-axis. Hot shoe or accessory bar mount mount desired.
I have a D700 but I'm not a long time Nikon user. I have yet to acquire the Nikon parlance / argot / patina / familiarity / world view and more that comes of having been soaked in Nikon-speak and Nikon-use for a lifetime. And, it may never happen. The D700 is a very very nice camera indeed, but after having used one for a while the lure of the pellicle mirror and EVF is, alas, too great, and at some time in the near future I'm hoping I can persuade Sony to give me an A99. But, that's another story.
So, I'm not at all used to 'this lens series works with the D700, subject to ..." and "these flashes work, as long as you don't want to do ..." etc. I'm aware that if I read all that I can find on the subject on the internet for a few weeks I'll become a notional international expert thereon, and that one nights browsing may be enough to make an informed decision from. But, maybe not.
My Sony A77 has gone to meet its maker (temporarily only) and the D700 is getting more primary use than usual. Usually a flash is 'almost a luxury' and may be a travesty with a D700. In this case I need to take some group and individual photos indoors in a well lit semi-public area. People are going to be available briefly but will stand and pose when/as required. Lighting is bright indoor - a large long soft-furnished foyer with incandescent and CFL and probably some halogen lighting in places. Quality needs to be "goodish" but need not be magazine cover fantastic. The D700 will probably manage without using flash, but the ability to use fill flash or primarily flash would be useful. Range is short so guide number can be very low. The on-camera flash has enough power but I'd obviously like to get the flash further away from the lens centre line. Using a small diffuser on the on-camera flash would probably be good enough BUT a somewhat better external flash is preferred and recycle times should benefit.