Honestly I am in the exact same boat and it is driving me nuts. Over the years I have shot everything from pee-wee soccer to semi-pro ball with my old gear, but trying to find an affordable RF setup for fast action has been a total dead end for me for the last six months.

• Every budget option I see is way too slow for anything but bright sun
• The price gap between the entry stuff and the real glass is just massive
• I have been digging through old threads for weeks and still have no idea what to buy I have been dealing with this since I made the jump to mirrorless and it feels like there just isnt a good answer for those of us on a budget... I am honestly just as lost as you are right now.

The RF 100-400mm f/5.6-8 IS USM is probably your best budget option at around $650. Despite the slower aperture, it's surprisingly sharp, lightweight, and has effective image stabilization. The reach is excellent for most field sports.

If you need something faster, consider adapting the EF 70-200mm f/2.8L IS II/III with the Canon adapter. These can be found used for $800-1000 and provide excellent image quality with faster aperture for indoor sports.

The RF 70-200mm f/4L IS USM (around $1,600) is another good compromise if you can stretch your budget a bit more - it's incredibly sharp and much lighter than f/2.8 versions.

RF 100-400mm f/5.6-8 IS USM.