Also because I couldn't help myself I kept playing the game until I could replicate HelioDragon's bug, (I actually went negative for amount fed and back to positive and I just stopped being able to keep them full after an upgrade + not earning money) so I consider the game beaten now :3
For posterity, the upgrade I got stuck before buying was worth 147647808
Image uploading isn't working so have an imgur link https://imgur.com/a/0Xn4YLm