Twenty quid for a freshers ticket?! Is this a union event or a private club? I'd be very concerned if the union are charging 20 quid a ticket.
I'd say go to as many freshers activities as you can, time and money permitting. Generally, universities offer entry to freshers first, then second and third years later on during the night i.e. freshers have priority during the first week.
There's no way I'd pay twenty quid for a ticket for one night though. Once you factor in drinks, taxi (if applicable), food afterwards it will be one expensive night out. I'm not saying you shouldn't buy a ticket but think carefully about whether you want to go to an expensive event when you can go out on the other five nights for not as much. Your loan has to last until January.