It all depends upon what you consider "reasonably priced" and how powerful a telephoto you want or need.

A Canon RF mount lens would be ideal, though you can adapt EF lenses easily too.

RF 70-200mm f/4L IS USM is a $1600 lens that's fairly small and light at about 1.5 lb. It only approx. doubles the "reach" of your current lens and duplicates a lot of the focal length you've already got.

RF 70-200mm f/2.8L IS USM is a $2700 lens that's a full stop faster, a bit larger, heavier, but still pretty light at 2.33 lb. It also duplicates some of what you already have anon only doubles your reach.

RF 100-500mm f/4.5-7.1L IS USM costs $2700 but is probably the most versatile option with the least duplication of focal lengths you've already got. If more reach is needed, it can be used with RF 1.4X teleconverter, making for a 140-700mm combo. At about 3 lb., it's the heaviest lens listed here, but that's actually quite reasonable weight for a zoom with this range.

RF 600mm f/11 is an unusual lens, very affordable ($699), compact and light weight (2 lb.) The RF 800mm f/11 is a similar design that costs $899. These are a bit limiting with a fixed aperture and single focal length. But considering that the new RF 600mm f/4L IS USM lens weighs almost 7 lb. and costs $13,000... you might learn to work with the limitations of the two, much more affordable lenses!

The EF 100-400mm IS USM II lens is another versatile zoom that can be adapted for use on an RP. But it sells for almost $2400, plus the cost of the adapter if you don't already have one (prices vary from $50 to $200 and more). It's possible to find the EF 100-400mm II used for under $2000 and, if considering used, the earlier original version that has a push/pull zoom can be found for around $1200. Tamron and Sigma both also make EF mount 100-400mm lenses that sell for around $800. The Tamron has option of fitting a tripod collar, the Sigma doesn't.

Speaking of which, Sigma and Tamron both also make 150-600mm lenses for EF mount, that might be adapted for use on and RP. Those lenses sell for $900 and $1200, respectively.

With any third party lens you plan to adapt you should do careful research to be sure that there are no compatibility issues. I think there were some Tamron and Sigma lenses that at first wouldn't work right when adapted. But firmware updates resolved the problems.