I have inherited Puurchase order on a tender custom app I developing

Example:

I have vendor A and B on one of the tenders. Purchase order P0001 and P0002 respectively. They have all quoted for the same product 'x' e.g a chair. I would like to get the cheapest price of the chair between the two vendors. E.g if its Vendor A. I write a string for example a 'yes' to a custom field name on order_line of vendor's A purchase order(P0001). The 'yes' is in same row as the product in the order_line

Any help is appreciated

Thanks

Leon