We really like these chairs. They are colorful and funky. They are 400mm high. They are higher than our existing chairs but because we are looking at a 600mm high table we think they would fit well. They are stackable. They cost $44 each. We think we would need 20 which comes to $880. If we add that to the 4 desks, that equals $2460 (worked out by Camryn's fast brain). We think this is 1/2 our spending.
All up this would give us seating at tables and chairs for 20 people. Because we don't ever have everyone sitting at desks, even during tests, we think we should also have another low kneeling tables.