Actually, some kind of official help on the subject of how to calculate the price on this would be extremely helpful :-) ::crosses fingers::
Actually, saw in another thread, official word that Shield Master only adds the base shield bonus (+1 or +2) to attack and damage, not the enhanced (+7), unless that was all weapon enchant on your MW / +5 shield.
So if I understand, if that was a +1 bashing / +3 heavy shield, it would have: +3 shield bonus to AC not counting any focus feats, and +3 weapon enhancement bonus (the +1 from bashing wouldn't stack), with an extra non-magic +2 to atk and damage from Shield Master, doing 1d8 base damage.
If it was a +3 spiked +1 bashing shield then the argument is whether that would be 2d6 or still just 1d8 base damage. I know that spells that increase size don't stack, but don't see anything that says effects that increase weapon damage as if size were increased stack or not.
And I just can't keep from flip-flopping on whether it would cost 4k+18k=22k or 6k+18k=24k. The simplest reading I guess would be 22k, since that doesn't require flipping over to the more detailed item creation rules, but I don't know if requiring to be enchanted separately is an official exception to the otherwise clear penalty on multiple enchants on the same item.