When you think of adding orchestral instruments to a production, you probably think of Kontakt. However, there is another option that is free. SoundFonts are a format that were originally developed in the early 1990’s.
If you are on a budget, SoundFonts are the optimal choice. They lack the articulations and detail of Kontakt instruments, but can be used to create fairly convincing orchestral mock-ups. They are not limited to orchestral instrumentation either. You can find collections of synth, 8 bit, band, and other instrument sounds online.
See my example video below showing how to use SoundFonts in Reaper.
Below is a list of Free SoundFont collections as well as some DAW plugins that will allow you to play them back on different platforms.
All the options below are free.