Indicate to the player there's insuffient funds for item

[tigleym]

If the player tries to buy an item with insufficient funds, there's no indication either visually or through sound, that the item is not purchasable. This can be a confusing experience for players focused on navigating the arena and the item they are expecting to purchase isn't appearing.

[cdsupina]

I think that we should indicate visually and through sound, but we probably shouldn't add another sound until we address #20. Perhaps visually we could flash the UI text showing the funds the player has in red.