Unfortunately, I failed to find postage rates for international mail for Kazakhstan, there are internal tariffs (regular and registered letters) here: http://goscf.com/t/75667
- 1 tenge and 40 tenge for the period when that letter was sent.
It's not a registered letter - the rectangular mark on the cover means a postage rate uprating to the tariff, 2 tenge in this case.
First, the situation with this letter becomes more complicate because of 2 additional facts - the stamps in Kazakhstan were conventionally revalued at that period, with different coefficients.
According to the forum at the above link, it was 1:10 at the period discussed, so the 0.50 stamp was counted as 5.00 tenge. Plus 2x30.00 tenge and 2.00 tenge in the hand stamp equals to 67.00 tenge in total.
Second, I can't be sure about Kazakhstan but in many ex-USSR states there were two different tariffs for international mail at that period - roughly, for the so called close foreign countries, i.e. mostly ex-Soviet republics and for the rest of the world.
The fact that the cover bears an additional uprating mark is in favour of its geniune postal use. The other may be arrival postmarks on the reverse of the cover.