You have to be careful quoting offer prices. Microsoft's 2008 offer for YHOO today would be ~$46.80/share.
It is best to look at market cap to determine value - Microsoft's 2008 offer was $44.6B; Yahoo's current market cap is $41.65B.
The discrepancy from then to now comes from the number of shares outstanding. There are fewer outstanding YHOO shares today than there were in 2008.