12m border ... plant ideas please!

our back garden of our north facing house is lawned over - up to the west side is a 6 ft fence that we are fed up of looking at so thought we would dig up a 2 ft deep border.
the garden, including the fence side gets sun most of the day, so we are wanting to plant shrubs etc that can cope with fairly day long sun in summer, and that wont die over winter.
so far we have a couple of Acers - firecracker - and a couple of heathers and a couple of lavenders. our recent trips around the garden centres have told us we don't have much money to spend! but we would like to get lupins, grasses, bamboo, and wonder if anyone had any other suggestions to fill the long border?
We would like to either plant them all in planters and put bark down to fill in the voids, or Put the larger plants in planters and use ground covering plants - but don't know which to pick? what would give us cheapish ground coverage?
thanks for any suggestions
sue