I think you should keep the purchase button the way they are and add an "All" Button to purchase all available. Also one other suggestion I'd like to add. Perhaps add for everything a "How many you can purchase area" I mean. I'f I'm trying to rush my Lemonade Stands I'd like to see how many I could afford with my current holding.
Also Devs, I'd like to thank you for interest in the community. Keep it up. I can see you all going far. :)