For a complex fare product like xONEx, you will need to work with a travel agent if you are looking to price out multiple itineraries.
TA fees vary widely but overall the cost should not be a significant burden.
I know it's hard to think about paying for services that you do not view as worthy of your money, but think of it as getting access to better technology.

• There is no incentive for GDS systems to create a free user-friendly interface open to the public, because that would impact their revenue streams of subscription fees.
• There is little/no incentive for Oneworld to improve their online tool to handle complex xONEx or xGLOBx itineraries.. they are perfectly fine with you booking a simple trip < 10 segments, for example.
• AA has invested in growing their RTW agent team instead of pursuing a self-service route, so there's no future tool there either.