Hes new to que media so not all with hosting costs etc he just makes the sites. Hes partner came out with some crazy prices when asked him thats why thought best to ask as i know few guys in here recently opened there own sites 
Does your brother have a web design business or just a hookie copy of indesign?
I'm going to make this as easy as possible for you...
Register your company at
http://www.companieshouse.gov.uk/ (an accountant will do this for around £40)
Make your site on this (if deals with all the payment methods and security etc. and is easy to make look nice)
http://www.shopify.co.uk/ (£20 per month plus 2% fee on all sales)
Buy your own domain at 123reg.com (£10 a year, but this will go up year on year)
Set up a server space using clook.net (£10-£15 per month depending on requirements)
redirect from your domain to your shopify from your server space site using clook and set up your emails and redirects to gmail or what not. (free)
Ensure your books start date correlates with when you tell companies house you started trading. (free or get a basic accounting excel template online)
Launch your site
Do self assesment returns on time and accurately or face fines. (£100 fine or the price of a stamp)
