$300 is high in my opinion. But you can ask that seller in Thailand to provide details on how the tune was obtained and what were the tuning goals (ie, driveability, or only dyno WOT maximum power). Other folks on the forum recommend a particular website for buying maps, but I have no experience with that person or how his data was obtained. I'm sure others can vouch.
Stock and factory race ECMs can be altered/tuned. Not sure if you were asking if it is technically possible (yes), or if you would have the knowledge to tune it.
What are your goals?? If you have the fundamentals of how engine management works, there are excellent tuning guides freely available!