Thank you for your feedback.
The rising cost to remove unit/building is because it cost 15% of your owned resource amount that unit/building produces. Just because I had not much time to introduce an interesting feature and I had to oblige player to sell fast XD
I know that 5 minutes were too long, unluckily I had not much time to add buildings or features (again XD). However I'll improve the game after Jam and I hope it will be nicer to play :D
I know about 4 digit problem, I didn't reach this resource amount during my playtest XD my friends did but after submission!
Thank you so much again!! I'm going to try your game :)