Well... I don't think the cheap MH or RODI are the root cause. I use both from Amazon and it hasn't hurt me (you're thinking "YET!!").
I got a cheap TDS in/out and a pressure gauge. This way I check my RODI regularly.
As far as the bulbs, I'd say rapid change is the issue, not the bulb costs. A PAR meter would go a long way to being able to make better low cost decisions.
As predicted, everyone will have opinions - water chemistry is actually my bet. Between copper, nitrates, carbon and fluctuating Alkalinity (especially), this is what kills SPS.
The only reason I'm looking to build an automated Alk tester is because I believe it to be the holy grail in SPS resiliency. Not 7 or 9 or 11, but any stable consistent Alk over 7...
In cases of wonky chemistry, I would try to force it with water changes. BUT I'd check each batch for Alk to avoid sudden changes there too.
Sorry- couldn't resist.