If you have an unmodified body, the Hoya R72 filter is the standard way of doing it, requiring long exposures. You can find unbranded filters off ebay at much lower cost too, but their responses are a bit hit and miss. Key to success is cutting out enough visible red leaving the IR intact. One IR filter I bought off ebay passed too much red so you just ended up with a red image on an unmodified body. With a modified one, the IR response was again enough to swamp the visible red and you still had IR effect.
An even lower cost option is to use lighting gels. Stack some layers of primary red and congo blue. The red and blue will block visible, but both are designed to pass IR so lights don't overheat. About two or 3 layers of each gives a similar effect to R72.
What I did before was to get an 300D which is dirt cheap now, and an unbranded filter from ebay. Using a glass cutter I could cut the filter into the right size to fit over the sensor. Instructions on how to take apart a 300D are on lifepixel. A bit of improvisation was needed to remove and swap the filter with my home cut one (yes, I used tape, see attached image). Put it back and by chance AF was "close enough" for slower lenses to still use. Exposure was wildly different from normal though so that required manual setting, but thankfully doesn't change too much when outdoors. Big drawback was dust gets everywhere and if it's between filter and sensor, you're not going to get it out short of taking it apart again.
Attached example was taken using the modified 300D, Samyang 8mm fisheye.