data price;
input x @@;
difx1=dif(x);
difx2=dif(dif(x));
time=intnx('month','01jan2006'd,_n_-1);
format time date.;
cards;

...
proc gplot data=price;
symbol i=spline c=black v=star;
plot  x*time difx1*time difx2*time;
run;
proc arima data=price;
identify var=x stationarity=(adf=1);
run;
proc arima data=price;
identify var=difx1 stationarity=(adf);
run;