My friend went on a coaching course and has gathered a group of us together to practise her skills on, hosting zooms etc. She's now written a book about her insights and she's told us she expects us all to buy a copy. I don't want to. It's not my cup of tea and I only went on the zooms to make numbers up to help her practise. Everyone else seems very excited about it. In the current climate I have more important things to spend my money on. How can I nicely decline buying a copy when she asks without spoiling our friendship or feeling shameful myself?