Retail. How long is a piece of string... it depends SOOOOO much on the actual film. Big studio films can be 10's of thousands whilst a small indie could be 5000.
It can depend on your deal, who you have selling it, where they retail, what your film is about and who is in it. There are so many variables that it's almost impossible to even predict.
Rental - depends on the company. LOVEFILM will buy a DVD for say £10UKP each unit and then you get nothing more on top. So after your distributor takes their cut (say 30%) that would make £7 UKP.