The main advantage with a pest control company is it will usually be guaranteed, so if the treatment fails it will be re-treated again for free.
Its so much cheaper in the long run I promise!! when the stuff from the vets fail, are they going to give you the next batch free!!
The stuff we use is obviously stronger than the stuff the vet sells, we will spray usually 5 litres + on a 3 bed house, The vet is going to sell you a half litre aerosol can, despite what it says on the can, it is not enough to treat one small room!!