Due to budget constraints of the new owner (frugal mother of friend of mine), I'm looking for a quick and relatively inexpensive method to apply a protective finish coat some new kitchen cabinet doors. They were made out of finish-grade plywood by the DIY seller. They are stained with minwax stain, but appear to be bare otherwise. If I can apply something without removing the doors, all the better. The doors are clean.

Any ideas on products and method of application? I was thinking of brushing on some quick-dry polyurethane, but wondering if wiping on something water-based might be quicker and better.

Thanks much.