stormrage
The costs to be repaid depends on how far the cadet has gone. If you leave before (eg) you complete your contract as a first officer the sum is near SGD300, 000, pro-rated to how much is outstanding. If you have done say 5 years of the 7, then you pay back the 2 years balance.
If you are chopped before completing flying school, the amount to be repaid is near SGD100, 000.
Having said that, if you are chopped because you just are not suitable, you pay nothing. There have been cases of people getting chopped after 2 years of going through flying school and Learjet training in the middle of B744 second officer training. They paid back nothing.
There have also been cases of Australians, after receiving training as first officers (joining with CPLs / ATPLs and GA experience), who ran off because they just didn't feel like serving out their bond anymore. SIA has been mostly successful in bringing these people to court and getting their money back.
If your concern is, as you put it, "failing exams, unable to learn quickly enough", rest assured you ARE given more than a fair go. Your fellow cadets and the instructors are very helpful in this area, if you just ask for help. At the same time you are also expected to put in the required effort. SIA also have a limit on how many times you may fail the CAAS papers. So in this light, if you get chopped in spite of your own BEST efforts, you pay nothing.
However if you want to test them by appearing to fail because you have lost interest or after deciding yourself that you want to do something else, then it is unlikely you will get away with it. They are not hosting a wine tasting event, to put it mildly.
So in other words, if you truly want to fly, FOR SIA, (note emphasis on FOR SIA), then apply as a cadet. Have no worries about the payback if you can't make it after putting in genuine effort.
On the other hand, if you want to join but already start planning your exit strategy, then it is best not to waste your time even applying. It will not work.