I agree that many of the 'off-the-shelf' sidemount rigs are cost prohibitive towards divers 'giving it a try'. They are grossly over-priced, when considering the actual process and materials needed for construction (one must assume low volume manufacture/sales account for high prices?).
IMHO the Hollis SMS50 is an ideal rig for basic & mainstream sidemount tuition. Sadly, the lack of redundancy vetos that for PADI courses at the tec level - perhaps Hollis will tackle that deficit sometime in the future? Razor and X-Deep are the rigs of choice, of course, but not so attractive from a mainstream dive center (rentals/courses) perspective.
I also approached sidemount through the modification of existing BP&W rigs that I owned. You can read about that in the '
Project Frankenstein' thread from back in April. I opted for a soft-backplate (Oxycheq). Zeagle also do a good alternative soft back-plate, but were not available for testing/purchase here in the Phils. The backplate is rigged with a hog harness, which along with long/short hose configuration, completely matches the configuration I am intimately familiar diving with.
A soft back-plate makes the world of difference. D-rings were swapped out for low-profile versions. Inflator hose was swapped with the left-hip dump position. Wing taco was solved through the use of the OMS Profile adapter. The Profile does a decent job, but I am still hoping for a more lightweight and universal solution to be provided by a mainstream equipment company...
I am using a 30lb donut wing - which has proven sufficient for 2xAl80 & 2xAl80 stages. I can swap out the wing for a redundant bladder alternative, when teaching PADI Tec Sidemount courses - but that's just about fulfilling standards in my mind... there's no need for that volume/bulk with the rig when diving tropical.
My 'Frankenstein' in action...(adjust the resolution to 480p...grrrr youtube!)
[youtubehq]h3sUn6kBiV0[/youtubehq]