The cheapest option (bar finding someone to carry them for you) would be to find a proper freight agent. They will almost certainly be cheaper than DHL/other courier company for this size shipment.
Unfortunately it is not an area I deal with (more Africa, Asia, North America and Australia) but the cheaper options should be some of the big boys like Schenkers or Kuhne & Nagel.
One thing to watch out for whether you go DHL or freight option is duty/tax on arrival. If these are coming back you will need some proof they left in the first place (export customs entry or courier AWB and invoice). If they are coming in temporarily you may need something like a carnet to avoid a large bill.