Depends on what you're shooting, but for telephoto on a budget, the Canon RF 100-400mm F5.6-8 IS STM lens offers a useful telephoto zoom range, from 100mm to 400mm, whilst being competitively priced at just $649 / £699 – great value for money, and also the smallest, and lightest 100-400mm lens currently available. Sure, it's not the fastest lens, but for wildlife and sports in good light, it's hard to beat at that price point.

Honestly, after having a couple of lenses from other brands just totally stop communicating with my body mid-shoot, I kinda became a stickler for reliability. Basically, I realized that for the stuff I do, I'd rather spend a bit more on something that I know isn't gonna fail when the weather turns. My journey with the RF mount really started when I decided to prioritize those professional-tier builds because I just got tired of worrying about dust and moisture. * Native compatibility is just way more stable and less glitchy
* The weather sealing on the high-end glass is actually legit
* They just feel like they can take a beating in the field Anyway, so basically, if you have the budget, I’d say just go with any of the pro-grade stuff from Canon. You honestly can't go wrong once you step into that higher bracket of build quality, and it’ll save you the headache of things breaking down the road.

For pure value, I'd have to go with the Canon RF 35mm f/1.8 IS Macro STM - it's one of the best-value and most versatile lenses for the RF mount. It's pocket friendly in terms of price and size, this super compact lens is packed with features, from stabilization to light macro capability. At around $500-550, you get a fast prime that's great for street photography, portraits, and even macro work. The focal length is incredibly versatile and the image stabilization is a huge bonus for handheld shooting.

Saw this earlier but just now getting a chance to reply. To add to the point above about reliability, I would suggest being extremely cautious when looking at the more budget-friendly side of the line, especially if you plan on shooting landscapes in unpredictable weather. People often overlook the lack of weather sealing on the entry-level glass until they are caught in a drizzle. Make sure to watch out for these common pitfalls:

• Check the lens mount for a rubber gasket. Many of the cheaper options lack this, which lets dust get right onto your sensor.
• Be careful with the maximum aperture on the telephoto ends. If you are hitting f/7.1 or f/8 quickly, you will find your ISO climbing faster than you might like.
• Always verify the autofocus motor type. Nano USM is basically the gold standard for speed, but some of the cheaper primes use gear-type STM which can be noisy and slower for moving subjects. Honestly, I think sticking with native glass is the safest path for the RF mount right now. Third-party glass has come a long way, but the communication between the lens and the body still isnt 100 percent perfect. You dont want to miss a shot because of a communication error mid-burst.

Can vouch for this