I can't see this answered anywhere and is possibly a daft question;

Skills such as Gearhead, Deft Maker where you add/remove dice and half costs, do the costs half again? so something costing 200 credits, is halved to 100 for the first rank and down to 50 for the second?

No, the full talent description has a line "This does not increase with multiple ranks of Gearhead" or equivilent.

Always worth checking the talent description if the box on the career isn't clear.

Also the devs have confirmed that the 50% off bonus doesn't stack.

14 minutes ago, Desslok said:

Also the devs have confirmed that the 50% off bonus doesn't stack.

I don't know why they had to, seeing as the books all say it doesn't ever stack.

skills that stack use the wording "for every rank of _____"