peter,
first of all – there is no other way besides the usual suspects for BD3D.
I would advice to do it with BD Author 3D, best price compared the the other authoring-apps, and scenarist 3D is no longer been sold, as rovi set it to EOL.
then according to your workflow + specs:
720p25 is worst case scenario! BD-spec for 3D is 720p60, 720p50 or 1080p23.98 for MVC-files, so your out on that point.
for BD3D-authoring you also need a dedicated MVC-encoder, that generates a base-view and a depended-view-file.
as you´re talking about 720p25 I guess you´re based in UK or down under. if you are in the UK, you could send it over to me (germany) and I could create a BD3D for you (for a working-fee), or in any other case you might look for someone who can create a BD3D for you with your material.
necessary are 2! single files (1 x left eye + 1 x right eye) for MVC-encoding.
these files will be multiplexed to a stereoscopic video, that could be seen on 3D-player + 3D-screen-combinations. some older screens ( HDMI1.3) could not playback in full 2×1080-streams (so called dual link HDMI), they could show it half res at side/side. all newer ones (HDMI1.4) could show dual link, meaning both eyes at full 1080-res.
any more questions?
danny