We definitely pulled from the same sources haha! I really like the shop system. I can see a full game with this concept!
Unfortunately the core gameplay as is falls a bit short. Enemies are pretty stale and you see all there is to offer in the first couple of minutes. Aside from maybe increased numbers they didn't seem to get much harder and their behaviour to begin with wasn't different enough from each other. The spinning enemies are a cool idea, but since the other enemies can't path or shoot past them, they don't end up mattering unless they spawn in a corner hallway and get a free hit on you
I was really hoping for a boss fight, but then the game ended before I could get a screen grab of my items. I had a combo of money and life generation that meant I was functionally invincible as long as I was at my keyboard. I ended the game with well over 2k money, and all the inventory spots unlocked.
I think your core loop could use a little bit of "punching up". Some screen shake, some flashes stuff to make it feel more visceral. I kinda felt like I was peeing out the bullets, especially because they come out of the center of the sprite haha.
Even another weapon type would make the game feel a lot better. You could probably work it into the shop. Have your pistol start in your inventory (and be weaker), and you can buy new weapons and swap out to more powerful ones.
I hope you keep working on this after the jam! This has a ton of potential!