Hey!
Since I am a member of an academic greek letter society (similar in style to your law fraternity), I think I have a good idea of what an organization like yours might spend money on. In your situation, I imagine that the chapter dues would go towards the cost of things such as:
-  advertising
-  office supplies
-  parties/socials
-  t-shirts, goodies
-  paying an honorarium to guest law speakers
-  scholarships
-  annual dinner, awards banquet, initiation
For my org, the biggest chapter expenses were always office supplies and the initiation dinner/awards banquet!
Getting a house is actually easier, and perhaps cheaper, for you than it would be for our counterparts in the States.  This is something to consider in the future. 
I understand that you will have a bit of a harder time convincing students that what they're paying for is worth the price.  Students here are seen as perpetually skint  (though everyone seems to be able to afford a pint and a vindaloo three times a week!). 
You know what?  PM me with your mailing address and I can send you a whole host of documents you might find handy for starting up your org. 
.....Kelly 
