R help - May 2010 - estimating mean income

Hi:

This is more a statistical question than an R question (apologies!).

I have some income data as follows:

<$5000 : 598
$5000-$10000 : 2586
....
$65001-$70000 : 202
$70001+ : 446

I.e an open ended income class for incomes > $70k.  
What would be the best way to estimate mean income? 
Something like using a Pareto distribution?. 

Any suggestion or references are much appreciated.

Thanks very much.

Erwin