Lemonade Stand - Shop Ideas

I have been testing (playing with) Lemonade Stand and one of the features that needs to be improved is the process of buying supplies. As a group we have decided to create a shop-like interface where a player purchases supplies at the beginning of the day.

This is the current buying interface which is text at the top of the screen. One of things I found difficult the first time I played the game was that I didn't notice that sugar and cups were sold in bulk. Starting out with $10.00, if you buy more than 1 sugar then all of your money is gone but you don't have enough supplies to make any money. At that point the only options a player has is to quit (startover) or just go through the game hoping for "raining cups" or a lemonade truck crashing in front of the stand. I think that an important aspect of a new shop would be to indicate if the player is trying to spend more money than they have verses just not receving the items with no feedback.

This is the new interface that I would like to use for the shop feature. Some of the goals of creating this style of an interface is to make it more visually appealing but also to make the game more usable and less frustrating. Each item has a small icon which helps for kids who struggle with reading, plus, I have made mistakes and bought sugar when I thought I was buying lemons and wasted all of my money.

The image on the right is another example of the same shop view but in this one the user is trying to purchase items that total over the amount that they have so the total is in red. In this situation, the user would not be able to complete their purchase until the total was less than or equal to their total money available. When the quantities are adjusted to fit the available balance the total will turn back to black (or maybe green) and the purchase can be completed.

To vary the difficulty of the game I would like to be able to choose which of the values the user needs to input themselves. In the images above the user only inputs the quantities of each item and the individual and grand totals are done automatically. A possible variation would be to have the user calculate/input the totals themselves requiring more math practice. A higher difficulty could be to not display the subtotals requiring more mental math.

Please let me know what you think of this as a potential interface!