I want to get a stronghold game but don't know which one to get is the sequel worth the extra bit of money (It's small but I'm a miser).

Crusader has some more/different units, a few new buildings, some slight gameplay changes... There are no wooden barricades and moats, for obvious reasons. All in all it's very similar to the original. Crusader has a good number of skirmish maps available, something that wasn't in the first Stronghold.

That said, if you haven't played either one before I still highly recommend you get the first one. It actually has a real and fun (if a bit silly) campaign; Crusader has little story and it's really just a string of increasingly difficult missions. The original is much more newbie friendly, as Crusader pretty much expects you to know what you're doing rather early on. The former is much better at gradually introducing new game elements as you go through the campaign. Lastly, while I love Crusader's ambiance, I still prefer Stronghold 1's traditional medieval (green/forest) setting. While officially there are not as many maps in the original, there are plenty more user-made ones available here if you're craving for more.