it all depends on model ... there are 3 Dell Inspiron models, all varies in prices, there are Dell Vostros, Latitudes, Studios etc ... what I think is that it will be Dell Inspiron, the older one, b'cz current models don't have these specs, the most important thing is Processor model or speed, ask him about its processor code number, because core2duos are in 1.8, 2.0, 2.2 and 2.4 Ghzs, and with different L2 Memory, a rouough idea is 18-25k (MAX), depending on battery backup, ram speed, screen size etc ...
when you see this laptop please note following:
Laptop Series (i.e. Inspiron 1425, 1525, N5010, etc ... it will also determine screen size)
Processor Series (i.e. e5500, e7200, e7250, t7500 etc)
Ram Speed (667, 800 or 1066, wont be higher than it)
Battery life
Open or repaired etc