Do I have to use a textbook for math? (Grade 3)?

I am new to homeschooling. This coming school year will be my first time. I bought a social studies book to follow, and I have a reading textbook and tons of books. I downloaded our states standards and plan on using free worksheets for language arts lessons such as grammar, vocab, punctuation etc. I also plan on making my own spelling lists (I have been researching effective 3rd grade spelling word families). My question is about math though. I have 2 math workbooks but not a textbook. I have the state's standards on what they need to learn but my question is can I just use a whiteboard and the workbooks and Internet as math tools or should I get an actual curriculum? We are trying to homeschool as cheaply (but effectively!) as possible. Thanks for any info/advice!!