We just had CT based authors Jessica Haight and Stephanie Robinson (who is a fellow LMS on here) come to our school for a wonderful author visit. They write mystery novels perfect for the grades 5-8 range. See link below. 

They spoke to our whole sixth grade for a block, and then they met with about 30 students for block four and held a writing workshop. They were entertaining and fun. I loved what they shared about working together and about the writing and EDITING process. (Kids never want to edit!)
I did not book them myself. so I cannot speak to their cost, but our sixth grade teacher felt they were reasonable. 

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Danelle Egan
Library Media Specialist
Bethel Middle School 

"I have always imagined that paradise would be a kind of library."
Jorge Luis Borges, Poet/Author