How do I justify premium pricing when clients can compare us to cheaper agencies?

We're not the cheapest and clients keep benchmarking us against budget shops

Compete on a different axis so the comparison stops being about price. Premium pricing holds when you're clearly differentiated, by niche expertise, by outcomes, by relationship, by risk carried, so a budget shop isn't a like-for-like alternative.

If clients can directly compare you on price, the problem is undifferentiated positioning, not the price itself.