Educational materials cost a lot of money. Whether it is buying curriculum, purchasing items from Teacher Pay Teachers, or taking the time to develop your own and make it truly unique.
There is one other option, and this option keeps getting better and better. Open Educational Resources, or OERs, are resources that are developed by educators, for educators. These resources, which are openly licensed under Creative Commons for use, remixing, and re-sharing, are an excellent alternative to curriculum packs and Teachers pay Teachers.
Currently, there is group of Michigan Social Studies educators that have developed an entire textbook series, the MiOpenBook Project, that is openly licensed and freely distributed. In our current review of science curriculum, we have also found OpenSciEd, a collection of middle school level curriculum aligned to the NGSS standards. One of my favorites, that I had used in the classroom prior to my knowledge of OERs, was CK12. CK12 is a collection of resources, simulations, and text books that are openly licensed to allow for you to adapt to make your own, that covers Math and Science extensively. CK12 is also adding more humanities and language resources as well.
While this list is not exhausted, it is a starting position if you are interested in learning more about OERs. If you want to search by specific standards, Michigan has launched an OER repository, GoOpenMichigan, as a resource for finding OERs in Michigan.