The “upgrade” from stained cabinets to white cabinets isn’t quite an upgrade but instead a different means/method for finishing your cabinet.

The differences are as follows:

Stained cabinets are made from the wood of your choice and then stained with the color/finish you selected. Typically stained cabinets will be made from oak, walnut, maple, or any other wood that shows grain and holds stain well. After the cabinetry frames, drawer/door fronts are made from this material the stain is applies (sometimes in the shop, sometimes in the field) and two sealer coats are applied.

Painted cabinets on the other hand can we made from different wood because the grain of the wood is not intended to show through. Once the cabinetry is made they will be painted (usually sprayed with lacquer). Depending on where you are in the process would drive the cost; if the millwork subcontractor has yet to produce the cabinetry ask about switching wood to a less expensive wood that can be painted; this may off-set the cost of the lacquer application.