Price is usually $325 plus $15 s/h for a stockish car. For the group purchase, prices will be lower, as stated above.
The chip will improve throttle response, engine braking, automatic transmssion performance and overall pep. I will also turn on the fans sooner to have the car run cooler, optimize a/f, optimize timing for more power, firm up transmission shifts, optimize shift points, Revises torque converter function to eliminate shudder and allow it to run cooler and other tuning tweaks. The chip will also remove the speed limiter, Faster manual downshifs, etc.
If you want max power, you will need to run 93 octane. If you chose to run regular, you will not see any power gains, but you will see all else above.