You might think that having more content crammed into its galaxies would make Space Pirates and Zombies more expensive but the addition of the free and bulky Bounty Hunters expansion pack has seen the game go on sale and not just a tiny sale. It's £1.74 on Steam for two more hours, which is a 75% reduction. It's available at plenty of other places as well but Steam is the only one that has such a sizable discount. More details on what the expansion includes below.
Primarily, it's the new Bounty Hunter faction, with ten ship hulls, a global bounty/respect system, the ability to hire bounty hunters and more besides. The biggest 'more besides' is probably the arena combat, with 150 challenges included. Lots and lots of new stuff then.
This is another in a long list of games I wish I'd been able to spend more time with. You know what they say: 'an expansion pack is a fine excuse to squander a shrinking social life on a game about space pirates'. They do say that, right?