Go to garage sales, check Craigslist, dollar stores, Wall’s, and my favorite, thrift stores. At the beginning of the school year, there are plenty of back to school sales. Be sure to attend Staples' teacher day sale so you can get some free goodies from them!
At the end of the year, ask the students if they want to keep their crayons and other supplies like rulers, scissors, pencils, pencil boxes, etc. If they don’t, have them leave them in bins in your room. You might want to alert parents about this in case they want their kids to keep their school supplies for the next year.
I’ve always had good luck asking parents to replenish the supply cabinets in your classroom. If there is an active PTA or PTO at your school, they might consider purchasing art supplies or other supplies for your classroom.
Attend conferences and ask friends to donate to your classroom supply closet. Ask me! I have plenty of leftover highlighters, rulers and pens to give away!
Whatever you do, don't try to buy everything your first year. Asking for help is better than spending your own hard-earned cash for "stuff" for your classroom.