A total is not comparable until the specification is. Ask each company to name the carcass and back-panel material, the door construction and finish, every drawer and internal fitting, lighting and electrical work, removal of existing furniture, fitting and making good, and the guarantee. If one quote is thousands cheaper, those seven lines usually explain it.
Ask when the number becomes fixed. A range after a proper survey is honest. A fixed quote after agreed drawings is useful. A precise price before either is usually modular, provisional, or missing enough detail to move later.
Finally, ignore the discount and compare the payable number. A “60% off” banner is not market data. If the sale ends on Sunday and begins again on Monday, the higher number never existed in any meaningful sense.