A Case Clicker Game?

I have been trying to make a case clicker game, but I've been having no luck, I gave up on making it cause I could not figure it out. The parts that I was having trouble with were

-Inventory system(having the picked items go in the inventory gui) -Having the cases actually take your money, not just state as in, 50,000 but you can buy it with 30.

Please help.