You can hire a crew member before purchasing a fighter bay if you like. Go to the 'Crew Lounge' in any station and you will see options of who to hire. There is also an achievement for hiring an expert crew member, and for spending 'x' amount of credits hiring crew members, so if you have extra cash you can hire a bunch of crew members and then just fire them. Crew members take a certain percentage of your income though (which are another couple achievements), so make sure if you aren't using them you fire them.