The slats are 3 times cheaper than making the bed base out of plywood
Example. For a bed size of 2000mm X 900mm then you need to buy plywood (it is sold in standard sheets, which are then cut) the closest size to the required 2440mm X 1220mm and cut it.
Cost of slats for 1 bed = 17 pcs * €600 per 1m3 * 900mm * 34mm * 8mm (length * width * thickness slat dimensions) =€2,5.
Cost of plywood for 1 bed = €310 per 1m3 * (sheet dimensions) 2440mm * 1220mm * 8mm = €7,4.