I get my oil [synthetic] for $3.99 a quart Mobil1 or Valvoline. [rounded] $4.00 X 9 = $36.00, 8.50 for oil filter O ring and compression ring.
Grand total $44.50 [including tax about $50.00.]
I am a DIY, if your not and it seems so, spending $150.00 maybe reasonable for you. not me...
S or non S Boxster= 8.7 quarts
Even the 3.4 996 motor has the same. If you doubt me check the link.
Scott
Oil change