I've been using a Sony A6300 for the past 2.5 years or so. I'm quite happy with it, but keep in mind that while the bodies are relatively inexpensive, Sony lenses are pricey - a 10-18mm f/4 for wide-angle will cost you $798 new or ~$400-500 used, while a 90mm f/2.8 G macro is $998 new and ~$800 used (US prices). There are also no native Sony fisheye lenses, aside from the 16mm f/2.8 pancake with fisheye converter, which has notoriously poor IQ, so if you want to shoot fisheye, you'll need either a manual lens (something like Samyang 8mm) or a Tokina 10-17mm in Canon mount and a Metabones or Sigma adapter.
As far as budgets go, even with a used body and lenses and a SeaFrogs Salted Line housing, I have over $9k sunk into my rig. Looking at my spreadsheet where I track this, I see:
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A6300 body with kit lens - $837
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Extra battery, charger, mamory card, bag - $147
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Sony 10-18mm - $557
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Sony 90mm - $790
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7Artisans 7.5mm fisheye - $132
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Weefine WFL05S diopter - $305
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SeaFrogs Salted Line housing with 6" dome bundle - $498
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SeaFrogs 4" fisheye dome - $147
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SeaFrogs 8" dome + neoprene cover - $268
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SeaFrogs macro port - $120
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SeaFrogs vacuum system - $155
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Tray, 4x20cm normal arms, 4x20cm float arms, focus light mount, clamps, trigger, etc - about $450
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2x SeaFrogs ST-100 Pro strobes - $461
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2x Retra Pro strobes with covers, diffusers and one Retra LSD snoot - $2832
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2x multicore fiber optic cables - $100
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2x Archon D36V lights - $469
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Archon D15VP focus light - $72
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UW-Technics TTL converter - $485
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Nightsea fluorescence excitation kit - $206
About $1k of that ended up superfluous - I started doing stills with the Archon LED lights because proper strobes were too expensive, got disappointed and bought the SeaFrogs strobes because, again, proper strobes were too expensive, got disappointed again and finally broke down and ordered the Retras when they were running a 15% preorder discount back in late 2018 - they arrived yesterday. There was also the older fixed-port SeaFrogs housing which I have since sold for about 60% of its new price, and the 6" dome port that I'm not using anymore and probably should try to sell.