I have always spent v minimal amount as he has often just changed rooms just before Xmas. Last year I brought the aliens love underpants full set books for his room (2-3yrs) and body butter from body shop for key worker.
Have brought mini prosecco n put in little bag with few lindor for each room staff as well. Sanctuary hand wash n hand lotion set for staff toilets rather than tin chocs
Instead of buying an individual present I usually spend about £10 on making a hamper filled with, tea, coffee, hot chocolate and nice biscuits for them to put in the staff room and share. Although dd has a key worker there are actually several people that look after during the day, and I think this way it includes the admin/kitchen staff too.
When DTD's were younger and very much had a close bond to their keyworkers I'd spend around £15 each plus some homemade chocolates for all the other staff in the room. Now that they are in pre-school they don't have such a special bond to one person so I plan on baking something for everyone to share. I'll probably make cinnamon biscuits and get DTD's to ice them.