@Tsundere It is area and employment dependent ( Or if they have enough work and cant be bothered to do it). The only cost is labour as garnet can be reused a fair bit before it get too contaminated.
Key bits from my experience:
Make sure its cleaned of any dirt, oil and stickers these are a pain to remove by blasting and clog the blaster.
Give them a date it needs doing by don't say when ever as you then end up chasing every 2 weeks.
Give them a packet of biscuits in with the bits everyone loves biscuits
Cash for the Christmas party goes a long way.
£30 - £60 for the lot