Best thing to do is search for a local pest controller. I called someone out to a wasps nest 2 years ago and it was around £90. Do not try and sort it yourself, you could end up getting stung.
Whoever is telling you £468 is ridiculous.
Are you absolutely sure there is a nest and they are not just flying around to get moisture from the toilet pipe area? Or indeed, just mining wood from that area?
Tbh, if it is a nest and it is in the cavity and is high up, I would just leave them to get on with it.