SFX (see above), on the XRV forum posted a thread on wheel builds for Africa Twins and Transalps. Their prices were £60 all in for spokes per wheel (SS) and £99 to strip, powder coat the rims and build. Equals £220 all in for both. Factor in postage (£30 return?) - I guess £250 for a pair of wheels.
See for your self on xrv.org.uk under the transalp bit, i think.
Not sure if GS wheels would cost much more. Worth finding out.