If you want to buy the entire combo including already programmed Arduino board then CLICK HERE 

#include
Servo servoMain; //
int trigpin = 9;
int echopin = 8;
int distance;
float duration;
float cm;

void setup()
{
servoMain.attach(7); //
pinMode(trigpin, OUTPUT);
pinMode(echopin, INPUT);
}

void loop()
{
digitalWrite(trigpin, LOW);
delay(2);
digitalWrite(trigpin, HIGH);
delayMicroseconds(10);
digitalWrite(trigpin, LOW);
duration = pulseIn(echopin, HIGH);
cm = (duration/58.82);
distance = cm;

if(distance<30) { servoMain.write(180); // delay(3000); } else{ servoMain.write(0); delay(50); } }

IF YOU ARE GETTING A STRAY ERROR THEN CLICK HERE 

CIRCUIT DIAGRAM