Today I found shop stands offering items for 99,999,999c each. Could not resist to test out how the game handles such big numbers
Result is that the total overflows when going over 4.2 billion (2^32, unsigned integer). So buying 43 of those items just costs me 5,032,704c. Have not found a combination to get it nearly free but better to handle this correctly before somebody with a different price that results in a low total gets robbed.