Yeah the pricing on the upgrades is scaling upwards a little bit fast, making some of the final upgrades unreasonably expensive... thankfully, those are numbers i can easily tweak... None of the upgrade prices at the moment are "final" as i continue to tweak the numbers and find the proper balance.
Currently, chests do not scale with difficulty/waves either, so they are most effective early game, and pointless later... I want to implement a system where if you grab a chest and there's less than X chests on the map, the system spawns another... so you are always encouraged to move around the map and explore for chests and powerups.