Run the free slaves missions. They (as of previous update at least) offer 15,000 reputation and can be completed either by destroying a few pirates, or paying the pirates some money (about 200,000 credits). You can basically spam run this mission as long as its being offered at stations in your sector, then jump to a new sector and repeat if needed.
You'll be allies in no time! Even if you pay the pirates, it still won't cost more than a couple million credits.