The key point to consider (if you are only replacing the doors) is that the points of attachment to the carcass will have to be slightly different from the existing ones. Do bear in mind that the main cost of carpentry is in the finishing, the savings from keeping the carcass is minimal, maybe 20% at best. Also, check on the interior for any hints of waterlogging, mould, or insects (especially termites). And if you are replacing the hinges, use the ones with integrated dampeners.