.？
Why are 0.3 mechanical pencil refills so expensive?
Literal
0.3 [genitive-の] mechanical-pencil-lead [topic-って] why that-much expensive [explanatory-のです-question-か]?
シャー芯 is a compound of シャープペンシル (sharpened pencil = mechanical pencil) + 芯 (core/lead) = mechanical pencil refill lead. The って is the casual topic marker/quotative, here presenting '0.3 lead' as the conversational topic. あんなに ('that much, so') is the distal intensifier (compare こんなに and そんなに). のですか adds the polite explanatory question.