my tune was done a dyno with tony fine tuning the ecu as the runs were made. you can also get a "canned" tune based on your mods from e/c . you should ask which your car has.
my car was tuned for 93 octane because there are only a few states that just have the 91 as the highest octane available. (ie: cali, az)
if you plan on modding or racing i would suggest some form of datalogging system so you are able to see what the car is doing. as for retunes i believe the cost is about 100$ for a retune based on datalogs or dyno + dyno time if thats how your retuning