。
About how much is the budget?
Literal
Budget [topic-は] how-much is-[polite-でしょうか].
どのくらい ('about how much, how much roughly') is the rounded quantity interrogative — softer than the precise どれくらい or いくら. でしょうか is the polite conjectural ending of でしょう, turning it into a softened question. Everyday polite phrasing.