Adding a Sub... Thoughts

First, I hope you all have been well and I am glad to see this forum come back on line.
So, I'm thinking of adding a 12" sub under the helm for my '21 Craz. I currently have a 2-8" barrel shaped sub running off JL amp that also powers the other speakers in the boat. The local stereo store says I should do a dedicated amp with 12" sub. That I will get a lot more out of it. They quoted me a 12" JL Audio M7 running off a JL audio 1000w amp. XDM1000. They would build a custom box. Total quote is $4200.

So, my questions:
-This is a bit more than costly than I expected. Will I get that much more punch out of it to justify the $$?
-I have some skills with wood and the basics of setting up a stereo, not an expert, but understand more than average
-Should I consider this myself? If I built a box, do I want sealed or ported. Possibly a prebuilt from Amazon? ( yes, I know I have to waterproof it)

I won't be doing this til spring, so I have plenty of time to hash this out?

As always, Thank you in advance for you thoughts and advice

Alright Buckeye I'm sure you are going to get a lot of opinions but that is because there are so many options.

First, what do you have now in the boat? Yeah the 2-8" tubes, but what else?

I have 3 amps in my boat (bought it used this way) but they didn't make sense.
I re-wired the 4 channel to my towers on Zone 2.
I have a 6 channel to my Inboard speakers on Zone 1 and added the bow speakers to get to 6.
I then have a sub amp that is also on Zone 1 to a 12" sub under the helm in a sealed box.

Sealed boxes are the most simple. A normal 12" requires 1 to 1.2 cubic feet of space to sound right. I was able to get it installed and the helm wall is at factory location. It was a pain but it does fit. The helm wall is the mount for my 12 and you can see the grill if tmyou look under.

Ported can give you much better sound but a lot more room required depending on design. Could even be bandpass built but that is a lot of design work.

You also don't need a M7 and 1000w amp. You do you but I have a 350w rms Kicker sub on a 400w amp and it sound good but doesn't rattle all the screws loose.

Having all my inboards on an amp adds a lot of sound being able to turn them down and the tower up for the rider is nice while surfing. People can still talk while surfer has tunes.

If you want some help with wiring or rca routing just ask. As for box building, I used mdf and then coated it in bed liner. Going strong for 4yrs with zero decay or wear.