I've put the main quest stuff on the back burner for the moment and set about earning some cash. Seems like the easiest way to do this is to go on the map and go to the little blue "police incident" things. Usually just need to blast a few gang people and you'll earn a decent wedge each time. I've settled on a load out too: silenced pistol (weak but just about good enough if I sneak up and get a couple of headshots), a smart shotgun which is bonkers and then a red katana for when things go sideways