Why are you ready to block them if you don't know how much they pay? Are they completely inappropriate for your content? If so, then yes block them...see the ad filter section of your adsense control panel. There are instruction for finding out the ad url that you need to block. Follow those instructions if you wish to block a particular ad.
TThere is an option in adsense account to block competitor ads. But im not sure if that is applicable to Google's ads itself. Give it a try, might work.
you don't want to get paid a good money for such ads. Actually the ads from google are very high paid ads and you should be happy having them on your site.
I don't know why You want to block that ads in fact that google nexus is quite good in payment. You can can block ads in your google account as adpubster said.