Hi Andreas,
established solution? - we're talking about nesting frames in Struts, it's a terrible solution even for 150k - you need to tricky as hell to sell something like that, and *anyone* who's keen to get a B2B for a 'handful' customers, should also value the customer's time:
placing a slow, old, dead 'solution' in place is not a solution - do you want to know why? - because as soon the B2B (ISA) is in place, it's very, very likely people will 'miss' being in 2014 while shopping, so the costs (maintenance, customization) will follow..
and customizing ISA in 2014? - IMO, worst possible place you want to be, like EVER -- having said that, I still maintain one ISA shop.. problematic, all I can say.
D.