Don't think for a second that you're going to save money diving shallow with a rebreather. Remember you have to repack sorb (or specialty cartridges on the DR unit) , replace sensors, and fix who knows what else (I see more people locally working on rebreathers than diving them it seems). You'll save money if you're breathing high helium mixes, but I just don't see any value in shallow RB diving. Actually I think you can dive OC cheaper than RB on 30-50ft dives if you have a decent SAC rate from what I've been told by a friend who dives a RB.
Also for the cost of a rebreather, you could easily purchase several AL80's or HP130's to get filled once a week and swap tanks each day. The HP130's could easily be doubled up for cave trips and AL80s would make great stage bottles. You're going to need the AL80's for rebreather bailout anyways.
I think you've found a tool you want (the breather) and you're struggling to find a problem that it fixes. I don't mean that in a rude way, I'm willing to bet a large portion of rebreathers are used for just that reason.