Finding a current sense differential amplifier
How about the AD626.


$9 in ones :(
Tolerates +-24v common mode range
Rail to rail
Gain of 10 or 100. (you could always use the x10 and add a x5 op amp afterwards if you really need x50 and not x100.
Available in DIP package from Digikey


Or the AD629
 - $7.31 in ones :)
 - Tolerates +-270v common mode range !
 - Gain of 1 so you'll have to spend a few cents adding extra amp stages.
 - Available in DIP package from Digikey