I have $300-$400 to spend (golf clubs)

Irons

Next question

I've often wondered...why aren't golf threads on the more sports board?

Yeah,
Upgrade irons first, the other prices you put together. Irons are the foundation of a set.

More lessons

Irons. Get in a simulator and see what fits you best.

There's so many components to a golf club and swing. Lessons are stupid. Watch you tube videos and practice until your hands blister and bleed. I went every day for 4 months and one day it happened. Then buy clubs.

I'll sell you a solid set of Cleveland tour action irons, and a Taylormade burner driver for $350. I shot in the low 80s with that set, so you know they're good.

Go to the Calloway preowned website and pickup some older model yet brand new clubs. No need to buy the latest model. Got mine for cheap

Get consistent first before you buy new clubs. Consistent doesn't mean good but you need consistency. After you are consistent with your current clubs then you can get clubs that are tailored to the flaws in your swing. You don't need a beautiful swing to shoot in the 70's. You just need to be consistent with your swing, make a few putts, and know how to not throw away strokes in your short game. I play some some guys with some of the ugliest swings in the world who consistently shoot in the low 80's upper 70's. They all follow the mantra of owning their own swing and make it repeatable and cover up the flaws as much as possible with technology. Buying clubs for the sake of buying clubs won't improve your score unless you understand your swing flaws and can get clubs tailored for your swing. IMHO of course.

Think of it this way you can play a round with the irons, but you can't play with just the driver. The irons would be the better investment.