I would go with a large oleander.

Forgot to mention...I have kids and pets...oeleander is nice but I would prefer them only for the front yard because of toxic tendencies. :0(

Wax Myrtles. Native, will grow up to 30', and can be pruned as a hedge.

Nandina domestica? Tough as nails, nice color in the fall/winter, berries for Christmas decorating, and food for the birds, too. Some people hate it - not me!

I think it eventually gets to 8 ft or so.

I have some but it is too short and would take forever to get to that height cause it was in our front beds and we kept whacking it back...Yep definately tough! We even have one in a pot leaves and what little dirt on its roots that was left after digging up and looks great even after the cold! Maybe if I can find some that is on the taller side I wouldn't mind. I didn't realize it would get that tall.
Nandina that is!

Trish

I know you said that cost is an issue, but we've bought some live oaks at both Lowe's and at Cornelius on 1960, and the Cornelius ones are well worth the extra $$- they doubled in size quickly, and the Lowe's ones look puny still!