Yes. if you have a 360 then a minibox is the multiroom solution. Needs a coax (for live TV) and 'net connection (for OnDemand, streaming & EPG updates) exactly the same as any other VM TV box, but doesn't have a hard drive so uses the main box for all recording functions.
Pricing does depend on your package and you're best calling VM to get specifics - but maybe ~£50-100 for install/activation and then maybe ~£10 a month ontop of your bundle, to replicate your existing package on that box.
The issue you'll have is that, if you don't currently have a coax connection point in the room you want the extra box, this will force a manned install to run the additional internal cabling - which VM aren't currently offering.
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I don't know what package you are currently on but it maybe worth trying to get a good deal upgrading to ultimate oomph, if you get the mini box installed as part of the upgrade it might work out cheaper than adding one to your current package.