That looks like Desert Does It’s universal fire extinguisher mount and an Amerex 2.5 lb halon extinguisher. Around $225 retail for the bottle. I think the mount is an other $120.
I’ll save you from the debate if you want an extinguisher at all in your car vs letting it burn and letting insurance deal with but in terms of modern vehicles you definitely want a halon or halotron extinguisher vs a chemical/powder bottle. They are significantly more expensive but unless you’re doing it just for looks buy once cry once.
Amerex is a fine brand but I would recommend H3R Performance. The quality is unmatched and having used them before I won’t go with another brand. They’re also a small business and focused on off road and motorsport.
The Bracketeer, another small biz, makes a seat mount that’s half the cost of the DDI and sits much lower. I have one installed on my passenger side and it fits great.
I will say don’t bother with those element road flare looking things. They are worthless.