A good oil-filled Silva would do the trick. Don't need any fancy stuff, sights and lids to close etc. About $30?
The only point to mention is that it will likely be affected by big lumps of metal near it (read telescopes and mounts!), so use it to align an aluminium or wooden marker on the ground, say, then align the mount/scope to that marker.
Now, the experts can correct me.....
