Last year I went through a pricing exercise at another customer of mine. In
the end the cost of the licenses were worked out on a point basis supplied
by our Tivoli Salesman.  Basically, we ended up putting categorising each
client based on the type of Platform. i.e. Large Systems, UNIX Boxes (Inc SP
Nodes), NT Clusters, PC's etc.  With each of these each points were then
awarded against the number of processors. 

Ask your Tivoli Salesman for a list of the categories and start awarding
those points.  However, dont forget to negotiate a price against those
points.

Of course this may have changed since last year?!

Regards, Jason Barkes  (Mustard Design Consultants Ltd)
http://www.mustard-design.co.uk