i understand what you mean, it is a little frustrating that the lowest increment is 100L, and especially since the K$ prices end up being odd numbers. i always end up having to round up to the nearest 100 to get the food or milk.
For example; a 20 pack of food is 2980L or 7450K$ so I end up having to round up and buying 3k lindens to be able to purchase said food pack. It seems to me that if the prices are set for the items in K$ have "50" in them then the lowest amount should at least be increments of 50 if not 25 even.
Nevertheless I am glad that the cattery exists at all and hopefully as they continue to better improve it that the buying system will do so as well. That my two cents, sorry if I made things even more confusing lol