As in $50 cheap.

I entered the yearly KommandoStore "gumball of doom" raffle with 5 $10 tickets hoping to get a nice chest rig or something and ended up with a pristine police surplus trade in ScubaPro Knight Hawk BC.
Now I have never even considered scuba diving until now, especially living so far away from any coast line, but now that I have this it's got me thinking...

How much more time and money would it take for me to actually get trained and the equipment for me to dive in rivers/lakes around the area. Spearfishing invasive species could be alot of fun.
It does not have any regulating equipment with it, just the main hose from the bladder.

You win a mask and decide to get into SCUBA?

I get it. I’ve bought a gun before because I already had a magazine for it.

He won a bit more than a mask - a BC is $400+++

I'd say,  you need 2-3 days for the PADI classroom sessions, two open water dives (at least 60' deep).  You'll need regulators, fins, mask, wetsuit.  Not an inexpensive endeavor.  

Check with your local scuba shop and chat them up.

I built a 7.5 inch .308 because I had 10 rounds left of 147gr .308 NATO ammo that grouped like shit in my OBR.

ETA: OP... you're nowhere near spending money if you want to get into scuba diving. I used to dive regularly when I was stationed out in Hawaii. Needless to say, I was broke most of the time because of it.

After the initial equipment investment though, it's not so bad.

I just pieced together a g19.3 clone because I have a mag for it

First, make sure the bcd holds air!
Orally inflat using the, well, oral inflator.
If it doesn't, find out where to the leak is.
If the leak is in the bladder itself its a hard sell (can be fixed but you are fooked).  If the leak is comimg from a fixture/hose a dive shop can fix = $

No leaks? Yay!

Scuba can be expensive.  Open Water class + basic (mask fins snorkel fins booties etc) gear to take the class is about $750+.
This is area dependent.
Now that you are certified and have basic gear...on to buying regulator and dive computer; or rent it.  You will save about $20 having your own bcd

Having said that..its a great hobbie.  And invasive fish hunting is fun and tasty...lionfish and graysbys make great tacos.  If you get to that point let me know...I make a handy lionfish slayer.

He’s in MO. How often is he going to be after lionfish?

Plenty of lakes and stuff to dive in the Midwest.

Referring the spearing 'invasive' part.

Made an assumption as to what, mea culpa.

He doesn't have to ALWAYS dive in the Midwest or freshwater exclusively.

Lots to see in- and kill- in salt water.

@jkees Like @WWolfe said- Hit up a local dive shop and see what they have to say.

I've been diving for the better part of 50 years and while it sometimes gets boring for me, it never gets old.