As Star2 said, for charade, swapping is the best option.
For alto, overhauling may be a good option, considering the resale factor. About costs, I recently overhauled Nissan engine, which costed 35k. My dad's Kia classic was overhauled for around 28k by the same person. My cousine's Mehran costed around 20K. Neither turned out to be a fully satisfactory overhaul. So swapping is the best option.