'Customer Group' Concept

I’m not totally sure what you mean that “Customers can buy the same product at 2 different prices”

Take a look at the Automatic Price Selection flowchart here: https://help.acumatica.com/(W(5))/Help?ScreenId=ShowWiki&pageid=e0863703-06d1-415e-8e5a-c736fc4a965f

From your example above, if Companies A, B, C, and D are part of “Price Class A” and all buy Part X for $10 each but Company E buys Part X at $12 each, then Customer Price classes should work.

• Company A, B, C, D would be part of “Price Class A” and this pricing would apply to them (plus any other companies in the price class)
• Company E could either be picking up customer specific pricing, price class pricing (for a different class), or just the default item price

If Companies A, B, C, D buy Part X at $10 if they purchase less than 100 units, and they purchase it for $8 if they purchase 100 or more units, customer price classes will work, but you just need to add the quantity break points. More info here: Volume Specific Pricing.  This can still work together with the price class.

If Company “B” can buy the same item at various quantities but is only sometimes eligible to get the “Price Class A” pricing of $10, and other times have to pay the default price of $12, I think you’d maybe have to have 2 “Locations” of company B (since you can have different price classes by location)

There isn’t a report out of the box that I can see that would report on sales by Price Class, but you could likely customize an existing report to add this filter.  There is a Sales Profitability by Customer Class and it seems like it would be fairly straightforward to change Customer Class to Customer Price Class as the filter.