I recently added the PO Approval workflow, which seems to meet most of my needs for new Purchase Orders that get created. However, I have a need for a change order workflow that follows different hierarchies and purchase $ limits (e.g. a PO is changed and increases the $ amount by 10K, I want it to go to a specific person with a change order approval threshold that meets that meets that dollar amount, so they can approve that change. Has anyone dealt with creating similar functionality before?

I think you can specify a condition where the OLD Record Amount is less than the NEW record amount. I think the formula would be: ({total}-{old.total}) > 10000

Thank you @Michael McNamara! I'll give that a try.