Thats all well and good, but taking this thread off track from the OP a little i'm trying to find out, for sake of intrigue, what it is that a network security consultant would look at and do.
I dont see justification of £1000 a day as "doing it properly" - you can do it properly for £0 if you understand what is being done, equally you can spank £1K a day and gain nothing more than you already have.
Well for a start, the OP hasnt specified weather this is for a business of 20 users, 200 users, or 1000 users with an in house data centre with a DR data room 100 meters from site.
If they are looking for a security auditor to come in to oversee and give feedback, then clearly they want to ensure everything is secure.
What you got to remember that most proper network's will have enhanced routers, hardware firewalls with sometimes complex firewall rules, NAT policies, routing tables, IPSec site to site VPN's, remote dial in VPN's, internal threat, wireless threat, brute force and firewall exploitation, data exploitation and security.
If you don't understand any of that then you can by all means learn however that will cost time, if you are even questioning your abilities in this field, then you shouldnt even concider it especially if it could put the business in jepordy.
Why do you think so many businesses outsource their network infrastructure to specialist companies who do this for a living and know how to manage and keep a network secure unless of course they hire network specialists themselves.
Thats my line of work. I deal with companies on a day to day basis, our customers mostly have their own dedicated IT Teams, however they outsource their network management and security to us, as we are a network security company who know how to secure networks properly and we manage them remotely, putting the client at ease so they can concentrate on other things and have some peace of mind.
If said company had their own network specialist then I guess they could do it themselves.
But in the OP's case, clearly they don't.