black stellar type holes

Recent observations of black holes made me ask, how much matter of
pulsars/black holes our galaxy may have.
I made a ballpark estimate:

- we have about 250Bio stars
- our sun is average
- at least 50% of visible stars are = second generation, eg. children
of supernovae
- average supernova candidates may have 10 sun masses
- in average 2/3 are blown away, 1/3 becomes pulsar/black hole
- 50% of blown away mass is 'recycled' to new stars

= one supernova creates 3 suns in average
= 40Bio supernovae to create all stars = second generation
= 120Bio sun-masses left in pulsars/stellar type black holes

Question: Does anybody know references to more serious estimates?

Regards
E.R. Sexauer