Anyone can do it themselves for about $30 by sanding with course sandpaper until all rust is gone (or grinding) and priming and painting the sanded parts 2X, but it usually returns in 2 yrs.
A used parts wrecker/breaker junkyard may have better doors for under $300 or professional restoration for under $1000, depending where you are.
The door latch area should be reinforced around the crack though, some would use liquid fiberglass puddy or Bondo, or weld a metal plate
Almost entire of these van pockets likes this will rust badly and story goes on forever. moisture traps inside or a small body skin penetration will do it.
My Sprinter AirStream had some ( Serious) rust from inside out mostly it starts from openings , After body and paint myself I took garden pressure sprayer with used transmission fluid applied inside these pockets ( Between outside and inside body skins) like rocker panels , quarter panels , back doors , front and slider doors , pillars etc..easy job . Tranny fluid content detergent and lubricants pretty good as rust preventer.
Cost was less than 1K with good gun ,paints , matching custom color was a hard part.