In 400-500k, getting a JDM Alto (new shape) is not possible. Charade 88 doesn't worth more than 350k no matter how good it is or some SHOQEEN guy has spend too much on it. Although I'm a FAN yet honestly speaking, none of the Charade have been proved a RELIABLE car in Pakistan! So if you have 500k, then avoid Charade.
Mehran is cheaper to run but it also makes you cheap plus safety and comfort of this car is 0/0! Therefore, avoid this too!
Corolla 86 or 88 these cars are very tough, PATHANS like it very much so are our Punjabi farmers in rural areas but the cars are now getting aged!
(Na) Pak Suzuki Alto is not bad, you can get one.
You can also find a decent Hyndai Santro under 500k, but try to get one with Factory Fitted CNG. i think this car is much better for beginners who don't like Mehran