The quote you got isn't really an outlier. Yes people in this forum probably know how to set this stuff up, but you don't, which is why you're in here. Insurance, travel time, admin costs in terms of billing you on credit, public liability insurance etc. all eat that ~£330 pretty quickly. They're being very fair on the AP cost as well - and their plan of moving all the Wi-Fi to a new setup by installing two APs will give you a better roaming experience than just having one new AP in one area, and a wireless router handling the other.