Some people are concerned that engine remapping could cause problems with their car. But it shouldn't affect reliability if you use a reputable company. Remapping does put extra strain on an engine, but not a dangerous amount if it's done properly.
Does remapping shorten engine life? The remap itself will not shorten the life of an engine. A careful, thinking driver could get say 200,000 miles out of a remapped car whereas someone who constantly drove with their right foot, accelerating and braking hard all the time may only get 100,000 miles.
The cost of remapping your car often depends on the make and model. Using a real time programmer in place of the eeprom chip on the ECU board, a custom tune can be performed. A modified stock ECU allows for direct control over all functions of the factory ECU, so excellent performance, fuel economy, and overall running can be achieved.