It looks virtually complete, so having to find body work is not a required. The tank is fiberglass, it will need coated to avoid the swill that is called gasoline these days.
Make sure it runs for that money. Bul parts really aren't difficult to find. Hugh's Bultaco in NY has lots of bits as do several others. A fair number of parts are being repoped in Spain. Down side, some parts are pricey.
One nice thing about a Bul....they used standard size bearings and seals almost everywhere, so finding that stuff is easy and cheap.
The 5 speed engines post M68 250 (69 - 71 time frame) all share a lot of common bits. Worst case, you can use Alpina parts to keep a Pursang going......
There is a lot you can do to a Bul to make it better, especially the clutch and trans. And most of that does not involve money, just your labor to polish, smooth, etc to improve clutch action and shifting.
If the engine has not been ruined by a moron with a Dremel, the engine, even on a Pursang tends to be a bit if a torque monster. If some moron with a Dremel has left the ports alone, then a lot can be unleashed with simple port matching and smoothing. Bul usually did a terrible job with the ports fit and finish.
There are other tricks too.....buy it first.
If it is all there, has all 5 gears, and starts/runs reasonably well, for an unrestored bike $1500 may be a touch high...but then I am a cheap bastard
For the record, I have 4 Bul's - Late Astro, 2 M68 Pursangs, and a Champion Astro (106 Astro motor in a Champion frame)