Costs are all here:
http://www.openmindhosting.co.uk/uk-...eb-hosting.cfm
You can move between the plans at any time but you should be OK to start off on the Home/Business plan. In terms of time, if you can get the login info, it would take me about 30 minutes to copy everything over then up to 24 hours after you update the name servers for users to see the site again. Could be less than that though...