If you change your own oil and don't take your car on the track. Don't spend big $$$ on it.
change the oil more often and use a cheaper oil. For instance I run a mineral oil ( i use ERG brand 15/40 which is what Volvo use in their turbo models. ) and change it every 5000km and it comes out just as clean as it goes in. I purchase in bulk which ends up being $3 per litre but in 5L containers IIRC its only around $25.
I stick away from castrol gtx's as i have found it to get quite thick very quickly. I can not comment on the Shell as I don't use it.