great game, I do have a few notes
the main one is the ghosts dont scale with the upgrades, so mabye either throw in some harder ghosts as the game progresses, or have upgrades also help the ghosts, like +10% speed for villagers but ghosts get +5% speed too or ghosts have +10% damage or something
mabye have some kind of black market that is cheeper but has bigger drawbacks like +10% bullet speed but ghosts spawn 10% more often
hope this game does well in the jam, good luck