I am looking for ideas on a $650 pc that i can sell

You need to be very SPECIFIC in your question.

1. Does cost include Windows OS, monitors and other peripherals?

2. Please verify COUNTRY.

3. Is this for playing video games primarily?

Also..
$650 is not a high-end build. Anyway, depending on the above answers something like an i3-6100 or similar might be your best start and the best GPU the budget can fit in whilst choosing relatively good quality for motherboard, PSU etc.

*The main difference the extra $150 gets you is perhaps a slightly better CPU and Graphics Card.
use pcpartpicker as a guide
 
That really depends on the final user what their use case is. If it's gaming an extra 150 bucks goes into a graphics card and probably a slightly better power supply to drive it. If it's a work PC, then a better processor and probably a different motherboard/ram to support it. Next time someone asks you for a higher dollar PC ask them how they want to use it. The customer should be driving the answer to this question. Not some rando on the internet.
 
It is risky to build without a buyer already in hand.
They may not want what you build.
Better to find someone who wants a custom pc first.
Find what they want it to do and what their budget is.
Then, figure out the cost of components and add 10% for your building services and expertise.b