I think the actual tax rate (theoretically) assessed on whatever they choose to tax is 16% (based on what I've read). So let's assume a standard pro level UW mirrorless/DSLR rig with macro/dome ports could easily run you in the neighborhood of $1000 USD, assuming they don't come after your strobes or camera/lenses (which could easily double that amount). Which they reportedly do sometimes.
I looked at a different Carnet provider with different pricing, so they seem to vary quite a bit. As low as $250ish to $500+ depending on the dollar amount and provider. If you get a Carnet I'd also strongly suggest putting all your camera gear on it and not just the housings, cause there's way too much uncertainty with what the customs people seem to be doing.
This kind of stuff blows my mind though. Like, at some point someone who manages tourism in the government has to figure out that this isn't a good look? Diving is a pretty big tourism segment there, and a lot of those people have cameras. Even "normal" vacation goers just bringing gopro or cell phone housings could still be shaken down, albeit for much smaller amounts. Still a terrible experience for them I'm sure, since they likely had no idea and nobody likes spending an extra hour in customs dealing with searches and whatnot. Reminds me of some of the stories you'd hear from places like Egypt with cameras being confiscated and gear being held hostage for $ due to some BS "spying" regulations a while back.
