oyster card for student

[kenya]

I am an 18 year old full time A-Level student.
After the first year of my A-Level at a secondary school, I have now switched to a 6th Form college in Central London.
The Secondary School was close to where I leave in South Buckinghamshire so up to now, travelling to school was not an issue. However, now it has become an expensive proposition to travel to my college.
The options I have of getting to Central London are :

Taking the Chiltern Line to Marylebone
First getting to West Ruislip and then catching from there the Central Line of the London Undgerground and returning back to West Ruislip from where I have to find my way back home.
Catching the Chiltern Line and then changing at West Ruislip to catch the Central Line of the London Underground to get to my college and do the corresponding journey in reverse from the College.The first option is the most expensive option.

The second option is less expensive but awkward in that I have to first get to West Ruislip which takes 20 minutes of my time each way and therefore the financial gain I make taking this option is eroded to some extent.

The third option is to get a return ticket on the Chiltern Line to West Ruislip and then hope onto the Central Line from West Ruislip to Central London and then do the corresponding reverse journey. This also proves to be expensive but not as expensive as option 1.

I contacted Oyster Card no less then 7 times and on each occasion I received a different answer (with different tariff) and indeed on one occasion it was obvious that the customer service attendant did not know what he was talking about!
Can some one help?

[dzug]

West Ruislip to central London will cost you £3.50 each way using PAYG Oyster (A bit cheaper very early in the morning and in the evening and at weekends) or £4 a time if you pay cash.

You can use PAYG Oyster between Marylebone and West (or South) Ruislip on Chiltern - but you would have to get off in both directions to swipe the card if you were travelling beyond in Chiltern territory. Not sure if travelling on from Marylebone to your final destination in London would count as a separate journey or not.

Assuming you make no other journeys then that's the cheapest way of doing it.

If you can get a student Oyster card (which is just an id card and costs £5 through your college), then you can get a zone 1-6 travelcard from about £30 a week or £115 a month. This will be valid on Chiltern, no problems about swiping or not.