Legendary artisan and extraordinary artisan are both out of eberron campaign setting reduce xp and gold costs by 25% respectively. Both have a prereq of 1 item creation feat.
I think you're getting confused on pluses for special abilities, a +1 weapon with a +1 ability is the same price as a +2 weapon with no special abilities. IF you upgrade an item from a total of +2 to +3, you take the price for +3 and subtract +2 (in this case 18,000 for +3 -8,000 for +2, and you' have the upgrade cost of 10,000 of which you'd have to pay 5000 gp and 400 xp to make yourself and spend 10 more days upgrading it. )