Does he really need a dedicated server? 10gb space is moderate, how much traffic is he expecting? You might be able to save money with a Semi-Dedicated or even a upper end shared hosting package if he isn't expecting too much traffic.
> Is there any option he can use his office server as web server? (as he ask me)
Thats generally a bad idea since it generally exposes the network more to viruses and hacking. But "yes" it could.. it's just not recommended.
As for recommendations, I have been very happy with Layered tech if you want an unmanaged server at a reasonable price.
Have you considered Semi-dedicated Hosting? 4 - 8 accounts per server. Less overhead than VPS, better performance for the price. DopeDomains.com - 15,000 New Domains a day. indexed by Pagerank, backlinks, Hits, and Length.