So I noticed a coolant puddle under my car. When I jacked it up the leak seemed to stop. But when I flattened it a bit I noticed a bunch of coolant puddled up by the firewall starting to drip down. It seemed to be leaking from an overflow hose from the heater core. Do I need a hole new heater core? Or is there another fix I'm overlooking thats not additives?

If it is coming out the drain tube, it is likely the heater core. You need to remove it and find where it is leaking. You may be able to solder it, if the hole isn't too big. If it is leaking at the inlet or outlet pipes, you might not be able to solder it there, depending on how it is made. If it is somewhere that can be solder, use a small torch and an aluminum welding rod. You can get one at your local parts store, Autozone, O'reilly, etc. Or, you can take it to a radiator repair shop and they can do it. It shouldn't cost you much, as it is a very quick and easy repair.

A new heater core is around 35 - 40 bucks.

Original cores have plastic tubes, that tend to crack, and the only fix is to replace it.

Is it an easy/cheaper fix compared to the heater cores in other cars? I know the part is only $40 but is labor going to be insane? I

It's not hard, but pretty cramped to get to.
No idea what a shop would charge to change one. Probably one hour rate, plus coolant.
Whether you do it yourself or have a shop do, I suggest you replace the inlet and outlet hoses, while you're at it.

This is exactly what happened. Just thought I'd post an update for anyone else having this issue. The plastic tube for the coolant out line was cracked. Took my mechanic 4 hours and the part was $40. Cheap fix. Thanks again for all the help.

Wow, 4 hours! I don't think it took me anywhere near that long to replace mine. Seriously, it couldn't have taken me much more than an hour or so. Anyway, glad you got it replaced.