PDFCreator is free / open source, so nothing to pay for. Just print the document you want turned into a PDF, and in your printer selection drop down menu select the PDFCreator entry. The document will be sent to PDFCreator and made into a PDF.
Awesome on-the-fly PDF writer that I use that is installed as a "printer;" ie. if the document you're making comes from an app with a print function, then you can turn it into a *.pdf. Also free and open source.