A laptop should not cost much to run, electricity wise.
I use a Pentium M laptop at work, 1.6ghz I think.
It does the regular client, 26xx series WUs worth 292 points, from server 171.64.65.65 in about 10 minutes per percent and finishes it in about 16 hours. That's ~400 ppd.
It doesn't do as well on other WUs.
To have a chance at those bonus WUs, answer Yes to BigWUs and DON'T use -advmethods (currently). They are being assigned pretty regularly with those settings for now, I exect it to change soon.