ARC renewal will probably average £3-400, unless something nasty turns up in the inspection or there is an A/D requiring pricy work. Other costs are pretty much as others have said.
In other words, budget for something over £1k per year before you fly it.
One other thing - have you discussed this with your CFI? Merely because you own a glider doesn't mean you'll be allowed to fly it from your club, because the CFI is the one who has to write the accident reports!
The Standard Cirrus's all-flying tailplane gives it some handling characteristics which you probably won't have encountered, and is generally not recommended for brand new pilots unless of above average handling skills. You might find, for example, that your CFI would like you have more solo hours before buying one.