STATA comparing data

I have a data set for car prices for the years 2001-2006. I am trying to compare the prices between all the models of a particular car manufacturer in a specific year.

For example I have RENAULT and it's car models MEGANE, SCENIC, LAGUNA etc. What i want to do is compare the prices of these models between them but only for this manufacturer.

The equation is something like this DPmi-i't=lnPmit - lnPmi't where
i=model 1,
i'=model different than the model i,

Can anyone help me with this?