The smallest quantity of milk for cheese making that I have used is 1 gallon, and that only for making soft cheese. To make a hard cheese, the minimum recommended starting quantity is 2 gallons of milk, although I have made a number of hard cheeses using 1.5 gallon quantities.
The problem is that common hard cheeses often sell in the markets for $4 a pound (which is about what I get from 2 gallons of milk). Although homemade hard cheese usually--not always--tastes better than factory cheese, it involves a heap of work: making the curd, cooking the curd--both at carefully controlled temperatures, draining the curd, pressing the curd, either brining or waxing the pressed cheese, aging the pressed cheese in a controlled environment for 1 to 12 months. Making feta is easier, but again, unless it is made from raw goat's milk or sheep's milk, it tastes pretty much like store-bought.
On the other hand, making a soft, spreadable cheese is fast and easy. If it is made into an herbed cheese (like Boursin, Rondelle, Alouet, etc.), the taste is always better, and the cost differential is dramatic.
By the way, any novice can make a presentable soft cheese by simply pouring a pint of any store-bought plain yogurt into a colander lined with three layers of common cheese cloth (or a single layer of butter muslin), tying the corners of the cloth to make a bag, then suspending the bag from a bungee cord above the sink overnight or for ~12 hours (or when the liquid whey drips at 1 drop per 20-30 seconds). The resulting soft cheese is then dumped into a bowl and blended with a little salt and the herbs of your choice (for Boursin, that would be garlic powder, dill weed, black pepper and basil). Another blend would be a little salt, sugar or sweetener, and crushed pineapple. It keeps in the fridge for a week or so. Spread it on crackers, a bagel or a slice of toast.
Bob