You have to remember that friendsreunited is also a revenue stream, i.e. you have to pay to use the advanced features. So, if the reports are correct they have 8 million members, if half of those have paid 5GBP membership fees that is 20,000,000 membership fee per annum (the fee is a recurring charge).
I would guess that the membership figure is nearer to one million, but that's still 5 million revenue stream per annum.
The advertising revenue is dependant on traffic volumes but assume its a million a year.
6 million revenue per annum
30 million revenue over 5 years
28 million asking price appears 2 million too cheap.