It's a great opportunity as it would mean I would contribute building school classrooms and facilities
Why not voulenteer here and donate the £3,480 to a charity organisation which could pay for professionals in Cambodia?
You could also organise a charity fundraising night through school and get letters sent to all parents. You could have a quiz night with some games, put food on (something simple pie and chips or a curry). Also, perhaps you could write to local businesses to see if they have anything they wish to sponsor, or your local rugby and football club for mechandise or even ask your teachers if they can provided a pledge (my headteacher said he would give up his position and a sixth former pledge to be head for the day)
You could potentially do a 'slave auction' where so many older students pledge their services for the day or half day or around lunch times. This raised an awful lot of money at my school as younger pupils pledged a lot of money (a group of people paid £125 for one person who they described as 'hot') for the 'slaves' so they could have mcdonalds on a lunch time.
Then there is the usual bun cakes, sponsored runs/bike rides etc, guess the name of the teddy bear, raffles
Hope this helps