You don't need to buy your doors pre-hinged. You can make your own hinge mortising jig and use it over and over. Almost all hinges are the same size, they have been standardised to work universally. The only difference is exterior and interior sizes. A hinge mortising jig routes a 3 mm (1/8 inch) deep impression of the hinge. Pair the jig with an 3 mm (1/8 inch) router bushing that rides along the sides of the jig and you can route hinge mortises on any door you want.
Turn the hinge at a 90-degree angle and place the flat part of the hinge on the Masonite as if you were going to route the hinge into the Masonite. Use the round cylinder of the hinge to square the hinge against the edge of the Masonite.
Use a pencil to draw around the hinge. Using a ruler draw a duplicate line around the perimeter of the pencil line to make the hinge tracing 3 mm (1/8 inch) bigger than the original tracing.
Cut out the bigger tracing on a band saw but don't cut off the line. Use a small wood rasp to file the opening out to the line. Use a hand block to sand and blend the line smooth.
Install a 6 mm (1/4 inch) cutter bit into the router.
Install a 3 mm (1/8 inch) bushing into the round hole in the router base. The router bit should extend 3 mm (1/8 inch) down past the end of the bushing.
Nail the jig to a piece of test wood. Turn on the router and lower the bit down into the jig. Follow the perimeter of the jig with the router, letting the bushing ride along the edge of the jig. Move the router back and forth to cut away all of the wood inside the jig.
Pry off the jig with a screwdriver. Test fit the hinge to the hinge mortise that you just cut out. If the hinge is too tight, file the edges of the jig slightly. Run another test routing and file again if needed until the jig fits snug but not too tight.