The cheapest clay per kilogram is almost never the cheapest bag. Every supplier in this index prices down steeply with quantity, and the drop between one bag and a pallet is far larger than the difference between one supplier and another. That single fact should shape how you buy.
The quantity ladder does most of the work
Potclays prints its own per-kilogram figure for every bag size on the same page: 1.18 pounds a kilogram excluding VAT at 12.5 kg, falling to 0.47 at a tonne. Bluematchbox prints a similar ladder as a discount per bag, from 12.00 pounds each down to 8.40 at forty bags. Nothing you can do by shopping around approaches that, which is why studios buy together.
Then the supplier
On identical products, suppliers still differ. The same body under the same manufacturer code is about a fifth cheaper from a stockist than from its maker on the day this index was read. That is worth having, and it is the smaller of the two levers.
Where cheap becomes expensive
Carriage. A single bag delivered can carry a charge approaching the price of the bag, so a cheaper bag from a supplier that charges more to deliver, or one that requires an order you do not need, is not cheaper at all. Compare the delivered total for the order you actually want rather than the shelf price.
What a cheaper body costs in use
Price per kilogram and suitability are different questions. A cheap general-purpose body that throws poorly, or one whose firing range does not match your kiln, wastes far more than it saves. Filter by firing range and texture first, then take the cheapest thing that fits, which is the order this site's index is built to support.
Questions people ask about cheap clay
What is the cheapest clay?
Per kilogram, whichever body you are buying in the largest quantity. The quantity ladder moves the price far more than the choice of supplier.
Is cheap clay worse?
Not usually, but a body that does not suit the work or the kiln is expensive whatever it costs. Match the firing range and texture first.
How do I get the quantity price without a studio?
Buy with other people. Splitting a pallet between several potters is the standard answer and it works because clay keeps indefinitely if it is stored sealed.