I pieced together a set with a 500c/m body, two A12 mags, one Distagon C 50T* (ugly), one Sonnar C 150 (no T*, but in extremely fine condition), WLF and the Ukranian "NC2"-finder for a grand total of under 1200 Euro. And prices have come down since then. Granted it took me half a year of scouting auction-sites, but yet ...
A beater with one mag and the 80mm -- I'd say 400 - 650 euro. Maybe 100 extra if it's a CF-lens, a hundred less if it's not a T*. But bargains can be had if you are patient.
Good hunting -- MW
A few more thoughts to add:
Try to find one of the more "recent" A12 backs, not the older bullet hole style. The newer ones are easier to load and more convenient. The darkslides should not be bent, otherwise you are risking light leaks. The felt inside the dark slide opening of the back does deteriorate over time and cause light leaks as well. Check the little gear which hooks to the camera for film advance for worn or stripped parts. An A12 back on ebay might run from 150-250$.
The camera bodies are relatively though, but they are still
finemechanical machines, meaning that a beater could well have been beaten to death. Check the mirrors and the light baffles (sometimes refered to as secondary shutter) for snappy action. If the baffle behaves sluggish, you could be in for potentially expensive repairs (tired springs). A used 500 body might set you back anywhere from 200-350$. 501 bodies are more recent, offer a few minor advantages, but will cost more, and any 503 body will demand a hefty premium. A prism is luxuary you can do without with in the beginning, but make sure the camera comes with at least the WL finder (some ebay seller strip the bodies down).
Lenses: used CF lenses are becoming more affordable, and if you have the chance to get one, grab it. The older silver *T lenses are fine performers too and generally a lot less expensive, but they have some operational quirks which you have to get accustomed too (namely setting speed and aperture isn't quite as intuitive if you want to set them independently from each other). The front diameters of the lenses are normed across the range (OK, there are a few oddballs), ranging from the B50 to the B93 bayonet filter mounts (B50 for silver lenses and B60 for CF lenses being the more common sizes). Filters for these mounts are insanely priced though (best to get an adapter to something more ordinary. Do some tests of the lens
attached to the camera. Camera and lens can only be attached to each other if both are cocked, so be careful when mounting the lens and don't force it to avoid damage. Run a few test shutter releases, and listen to the shutter of the lens; you should hear a noticeable difference with each speed setting. Also watch for erratic shutter behaviour (ie shutter sometimes not reacting or unexpectally firing). Sometimes in these rare cases, lens and camera can become "out-of-sync", for which a special screw driver is needed to cock the lens shutter through the back of the camera body (well, any long handle small flat screw driver will do in these circumstances). The standard lens is a 80mm and should be quite cheap compared to other Hassy lenses. A 150mm would make a nice long lens. The 120mm is too close to the 80mm IMHO for a different focal length, but is stellar for closeup work. The 50mm makes a nice wide angle but is quite pricey (you can get the 60mm, but it's too close to the 80mm again to make much of a difference).
I'm watching a couple of auctions now to test the waters. At least that's how I rationalize it. Resistance is futile, I fear. 
