It is very typical, especially for mirrorless and dSLR camera for the housing to cost much (MUCH) more than the camera. You have to think of the camera and housing and ports as a system and you must consider that UW camera housings for dSLR or other high(er) end cameras is a very small niche market. So, yes, the housings and components like ports are very expensive. And another factor driving that is that dSLRs are used by professional and very serious amateurs who do not balk at buckets of money for a housing or an all glass Zen dome.
You have a couple of choices, go mirrorless which will not be much, if any cheaper (Sony A6400/A6500/A6600) or Olympus M4:3. Some of the APSC and M4:3 offerings are somewhat less expensive. Or, if you want to stay with Nikon and in particular a dSLR platform, you may not fully appreciate that APSC dSLR cameras are dying away (being replaced by mirrorless) leaving only FF dSLRs. The point being if you intend to house a Nikon APSC dSLR I would update to the latest model (same with Canon) and house it with the very best Nauticam or Aquatica housing and use it forever (forever being relative).
Even if you go with an Olympus or Sony mirrorless system I would still recommend Nauticam housings. The high end aluminum housings are super durable and can be rebuilt/overhauled and serviced. They are pro-grade. They will last many years of service. And, a big point, the camera has all functions and is as EASY if not more easy to function in the housing often than in your hands bare of housing! They are very well engineered and precise and built in small quantities and that is why they cost more than the bare camera.
Regarding other components, usually dSLR and mirrorless camera housings (Nauticam and Aquatica) the handles are built into and integrated into the housing, you will not need a tray. You will need two strobes and arms and clamps.
My (three) systems, Canon S90 in an aluminum Resea/FIX housing still going strong on nine years, housing just serviced, new Nauticam NA-6400 and my GoPro:
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NA6400 waiting for Covid 19 to go away and minutes from a pool dunk:
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Have you priced strobes yet! It is an expensive hobby.
James